This patch fixes test failures related the date(1) utility.

In the long term we could add a wrapper function to detect valid options
for date(1) and use the variant which works on the current OS.

For now, this makes some tests pass and shows us where the problems are.

diff --git a/regress/cmdline/blame.sh b/regress/cmdline/blame.sh
index a9916124..243a3bc4 100755
--- a/regress/cmdline/blame.sh
+++ b/regress/cmdline/blame.sh
@@ -65,7 +65,7 @@ test_blame_basic() {
 	local short_commit2=`trim_obj_id 32 $commit2`
 	local short_commit3=`trim_obj_id 32 $commit3`
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 	echo "2) $short_commit2 $d $GOT_AUTHOR_8 2" >> $testroot/stdout.expected
 	echo "3) $short_commit3 $d $GOT_AUTHOR_8 3" >> $testroot/stdout.expected
@@ -113,7 +113,7 @@ test_blame_tag() {
 	local short_commit1=`trim_obj_id 32 $commit1`
 	local short_commit2=`trim_obj_id 32 $commit2`
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 	echo "2) $short_commit2 $d $GOT_AUTHOR_8 2" >> $testroot/stdout.expected
 
@@ -149,7 +149,7 @@ test_blame_file_single_line() {
 
 	local short_commit1=`trim_obj_id 32 $commit1`
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 
 	cmp -s $testroot/stdout.expected $testroot/stdout
@@ -184,7 +184,7 @@ test_blame_file_single_line_no_newline() {
 
 	local short_commit1=`trim_obj_id 32 $commit1`
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 
 	cmp -s $testroot/stdout.expected $testroot/stdout
@@ -213,7 +213,7 @@ test_blame_all_lines_replaced() {
 
 	(cd $testroot/wt && got blame alpha > $testroot/stdout)
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 	echo "2) $short_commit1 $d $GOT_AUTHOR_8 2" >> $testroot/stdout.expected
 	echo "3) $short_commit1 $d $GOT_AUTHOR_8 3" >> $testroot/stdout.expected
@@ -265,7 +265,7 @@ test_blame_lines_shifted_up() {
 
 	(cd $testroot/wt && got blame alpha > $testroot/stdout)
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 	echo "2) $short_commit1 $d $GOT_AUTHOR_8 2" >> $testroot/stdout.expected
 	echo "3) $short_commit3 $d $GOT_AUTHOR_8 foo" >> $testroot/stdout.expected
@@ -321,7 +321,7 @@ test_blame_lines_shifted_down() {
 
 	(cd $testroot/wt && got blame alpha > $testroot/stdout)
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "01) $short_commit1 $d $GOT_AUTHOR_8 1" \
 		> $testroot/stdout.expected
 	echo "02) $short_commit1 $d $GOT_AUTHOR_8 2" \
@@ -394,7 +394,7 @@ EOF
 	local commit1=`git_show_head $testroot/repo`
 	local short_commit1=`trim_obj_id 32 $commit1`
 	local author_time1=`git_show_author_time $testroot/repo`
-	local d1=`date -u -r $author_time1 +"%G-%m-%d"`
+	local d1=`date -u -d "@$author_time1" +"%G-%m-%d"`
 
 	cat > $testroot/wt/alpha <<EOF
 SUBDIRS = ext modules codedocs docs
@@ -421,7 +421,7 @@ EOF
 	local commit2=`git_show_head $testroot/repo`
 	local short_commit2=`trim_obj_id 32 $commit2`
 	local author_time2=`git_show_author_time $testroot/repo`
-	local d2=`date -u -r $author_time2 +"%G-%m-%d"`
+	local d2=`date -u -d "@$author_time2" +"%G-%m-%d"`
 
 	cat > $testroot/wt/alpha <<EOF
 SUBDIRS = ext modules pdns codedocs docs
@@ -445,7 +445,7 @@ EOF
 	local commit3=`git_show_head $testroot/repo`
 	local short_commit3=`trim_obj_id 32 $commit3`
 	local author_time3=`git_show_author_time $testroot/repo`
-	local d3=`date -u -r $author_time3 +"%G-%m-%d"`
+	local d3=`date -u -d "@$author_time3" +"%G-%m-%d"`
 
 	cat > $testroot/wt/alpha <<EOF
 SUBDIRS = ext modules pdns codedocs docs
@@ -469,7 +469,7 @@ EOF
 	local commit4=`git_show_head $testroot/repo`
 	local short_commit4=`trim_obj_id 32 $commit4`
 	local author_time4=`git_show_author_time $testroot/repo`
-	local d4=`date -u -r $author_time4 +"%G-%m-%d"`
+	local d4=`date -u -d "@$author_time4" +"%G-%m-%d"`
 
 	(cd $testroot/wt && got blame alpha > $testroot/stdout)
 
@@ -718,7 +718,7 @@ test_blame_added_on_branch() {
 	local short_commit2=`trim_obj_id 32 $commit2`
 	local short_commit3=`trim_obj_id 32 $commit3`
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit1 $d $GOT_AUTHOR_8 1" > $testroot/stdout.expected
 	echo "2) $short_commit2 $d $GOT_AUTHOR_8 2" >> $testroot/stdout.expected
 	echo "3) $short_commit3 $d $GOT_AUTHOR_8 3" >> $testroot/stdout.expected
@@ -788,7 +788,7 @@ test_blame_symlink() {
 		return 1
 	fi
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit0 $d $GOT_AUTHOR_8 alpha" \
 		> $testroot/stdout.expected
 
@@ -809,7 +809,7 @@ test_blame_symlink() {
 		return 1
 	fi
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit0 $d $GOT_AUTHOR_8 beta" \
 		> $testroot/stdout.expected
 
@@ -958,7 +958,7 @@ EOF
 
 	(cd $testroot/wt && got blame alpha > $testroot/stdout)
 
-	d=`date -u -r $author_time +"%G-%m-%d"`
+	d=`date -u -d "@$author_time" +"%G-%m-%d"`
 	echo "1) $short_commit5 $d $GOT_AUTHOR_8 X" > $testroot/stdout.expected
 	echo "2) $short_commit1 $d $GOT_AUTHOR_8 A" >> $testroot/stdout.expected
 	echo "3) $short_commit1 $d $GOT_AUTHOR_8 B" >> $testroot/stdout.expected
diff --git a/regress/cmdline/commit.sh b/regress/cmdline/commit.sh
index d2b9ef37..7ec03bec 100755
--- a/regress/cmdline/commit.sh
+++ b/regress/cmdline/commit.sh
@@ -1399,7 +1399,7 @@ EOF
 	fi
 
 	local author_time=`git_show_author_time $testroot/repo`
-	d=`date -u -r $author_time +"%a %b %e %X %Y UTC"`
+	d=`env LC_TIME=C date -u -d "@$author_time" +"%a %b %e %X %Y UTC"`
 	echo "-----------------------------------------------" > $testroot/stdout.expected
 	echo "commit $head_rev (master)" >> $testroot/stdout.expected
 	echo "from: $GOT_AUTHOR" >> $testroot/stdout.expected
@@ -1438,7 +1438,7 @@ EOF
 	fi
 
 	local author_time=`git_show_author_time $testroot/repo`
-	d=`date -u -r $author_time +"%a %b %e %X %Y UTC"`
+	d=`env LC_TIME=C date -u -d "@$author_time" +"%a %b %e %X %Y UTC"`
 	echo "-----------------------------------------------" \
 		> $testroot/stdout.expected
 	echo "commit $head_rev (master)" >> $testroot/stdout.expected
diff --git a/regress/cmdline/histedit.sh b/regress/cmdline/histedit.sh
index 8c612faf..f17f516a 100755
--- a/regress/cmdline/histedit.sh
+++ b/regress/cmdline/histedit.sh
@@ -152,9 +152,9 @@ test_histedit_no_op() {
 
 	# We should have a backup of old commits
 	(cd $testroot/repo && got histedit -l > $testroot/stdout)
-	d_orig2=`date -u -r $old_author_time2 +"%a %b %e %X %Y UTC"`
-	d_new2=`date -u -r $new_author_time2 +"%G-%m-%d"`
-	d_orig=`date -u -r $orig_author_time +"%G-%m-%d"`
+	d_orig2=`LC_TIME=C date -u -d "@$old_author_time2" +"%a %b %e %X %Y UTC"`
+	d_new2=`date -u -d "@$new_author_time2" +"%G-%m-%d"`
+	d_orig=`date -u -d "@$orig_author_time" +"%G-%m-%d"`
 	cat > $testroot/stdout.expected <<EOF
 -----------------------------------------------
 commit $old_commit2 (formerly master)
diff --git a/regress/cmdline/rebase.sh b/regress/cmdline/rebase.sh
index a3608c60..fb0d3cf6 100755
--- a/regress/cmdline/rebase.sh
+++ b/regress/cmdline/rebase.sh
@@ -153,9 +153,9 @@ test_rebase_basic() {
 
 	# We should have a backup of old commits
 	(cd $testroot/repo && got rebase -l > $testroot/stdout)
-	d_orig2=`date -u -r $orig_author_time2 +"%a %b %e %X %Y UTC"`
-	d_new2=`date -u -r $new_author_time2 +"%G-%m-%d"`
-	d_0=`date -u -r $commit0_author_time +"%G-%m-%d"`
+	d_orig2=`env LC_TIME=C date -u -d "@$orig_author_time2" +"%a %b %e %X %Y UTC"`
+	d_new2=`date -u -d "@$new_author_time2" +"%G-%m-%d"`
+	d_0=`date -u -d "@$commit0_author_time" +"%G-%m-%d"`
 	cat > $testroot/stdout.expected <<EOF
 -----------------------------------------------
 commit $orig_commit2 (formerly newbranch)
diff --git a/regress/cmdline/tag.sh b/regress/cmdline/tag.sh
index fdc7ff87..6e6e9148 100755
--- a/regress/cmdline/tag.sh
+++ b/regress/cmdline/tag.sh
@@ -137,11 +137,11 @@ test_tag_list() {
 	tag_id=`got ref -r $testroot/repo -l \
 		| grep "^refs/tags/$tag" | tr -d ' ' | cut -d: -f2`
 	local tagger_time=`git_show_tagger_time $testroot/repo $tag`
-	d1=`date -u -r $tagger_time +"%a %b %e %X %Y UTC"`
+	d1=`env LC_TIME=C date -u -d "@$tagger_time" +"%a %b %e %X %Y UTC"`
 	tag_id2=`got ref -r $testroot/repo -l \
 		| grep "^refs/tags/$tag2" | tr -d ' ' | cut -d: -f2`
 	local tagger_time2=`git_show_tagger_time $testroot/repo $tag2`
-	d2=`date -u -r $tagger_time2 +"%a %b %e %X %Y UTC"`
+	d2=`env LC_TIME=C date -u -d "@$tagger_time2" +"%a %b %e %X %Y UTC"`
 
 	got tag -r $testroot/repo -l > $testroot/stdout
 
@@ -184,11 +184,11 @@ test_tag_list_lightweight() {
 	tag_id=`got ref -r $testroot/repo -l \
 		| grep "^refs/tags/$tag" | tr -d ' ' | cut -d: -f2`
 	local tagger_time=`git_show_author_time $testroot/repo $tag`
-	d1=`date -u -r $tagger_time +"%a %b %e %X %Y UTC"`
+	d1=`env LC_TIME=C date -u -d "@$tagger_time" +"%a %b %e %X %Y UTC"`
 	tag_id2=`got ref -r $testroot/repo -l \
 		| grep "^refs/tags/$tag2" | tr -d ' ' | cut -d: -f2`
 	local tagger_time2=`git_show_author_time $testroot/repo $tag2`
-	d2=`date -u -r $tagger_time2 +"%a %b %e %X %Y UTC"`
+	d2=`env LC_TIME=C date -u -d "@$tagger_time2" +"%a %b %e %X %Y UTC"`
 
 	got tag -r $testroot/repo -l > $testroot/stdout