t9604: Fix test for musl libc and new Debian

CST6CDT and the like are POSIX timezone, with no rule for transition.
And POSIX doesn't enforce how to interpret the rule if it's omitted.
Some libc (e.g. glibc) resorted back to IANA (formerly Olson) db rules
for those timezones.  Some libc (e.g. FreeBSD) uses a fixed rule.
Other libc (e.g. musl) interpret that as no transition at all [1].

In addition, distributions (notoriously Debian-derived, which uses IANA
db for CST6CDT and the like) started to split "legacy" timezones
like CST6CDT, EST5EDT into `tzdata-legacy', which will not be installed
by default [2].

In those cases, t9604 will run into failure.

Let's switch to POSIX timezone with rules to change timezone.

1: http://mm.icann.org/pipermail/tz/2024-March/058751.html
2: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1043250

Signed-off-by: Đoàn Trần Công Danh <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sgn

t/t9604-cvsimport-timestamps.sh

@@ -3,11 +3,28 @@
 test_description='git cvsimport timestamps'
 . ./lib-cvs.sh
 
+test_lazy_prereq POSIX_TIMEZONE '
+	local tz=XST-1XDT,M3.5.0,M11.1.0
+	echo "1711846799 -> 2024-03-31 01:59:59 +0100" >expected &&
+	TZ="$tz" test-tool date show:iso-local 1711846799 >actual &&
+	test_cmp expected actual &&
+	echo "1711846800 -> 2024-03-31 03:00:00 +0200" >expected &&
+	TZ="$tz" test-tool date show:iso-local 1711846800 >actual &&
+	test_cmp expected actual &&
+	echo "1730591999 -> 2024-11-03 01:59:59 +0200" >expected &&
+	TZ="$tz" test-tool date show:iso-local 1730591999 >actual &&
+	test_cmp expected actual &&
+	echo "1730592000 -> 2024-11-03 01:00:00 +0100" >expected &&
+	TZ="$tz" test-tool date show:iso-local 1730592000 >actual &&
+	test_cmp expected actual
+'
+
 setup_cvs_test_repository t9604
 
-test_expect_success PERL 'check timestamps are UTC (TZ=CST6CDT)' '
+test_expect_success PERL,POSIX_TIMEZONE 'check timestamps are UTC' '
 
-	TZ=CST6CDT git cvsimport -p"-x" -C module-1 module &&
+	TZ=CST6CDT,M4.1.0,M10.5.0 \
+	git cvsimport -p"-x" -C module-1 module &&
 	git cvsimport -p"-x" -C module-1 module &&
 	(
 		cd module-1 &&
@@ -34,13 +51,13 @@ test_expect_success PERL 'check timestamps are UTC (TZ=CST6CDT)' '
 	test_cmp expect-1 actual-1
 '
 
-test_expect_success PERL 'check timestamps with author-specific timezones' '
+test_expect_success PERL,POSIX_TIMEZONE 'check timestamps with author-specific timezones' '
 
 	cat >cvs-authors <<-EOF &&
 	user1=User One <[email protected]>
-	user2=User Two <[email protected]> CST6CDT
-	user3=User Three <[email protected]> EST5EDT
-	user4=User Four <[email protected]> MST7MDT
+	user2=User Two <[email protected]> CST6CDT,M4.1.0,M10.5.0
+	user3=User Three <[email protected]> EST5EDT,M4.1.0,M10.5.0
+	user4=User Four <[email protected]> MST7MDT,M4.1.0,M10.5.0
 	EOF
 	git cvsimport -p"-x" -A cvs-authors -C module-2 module &&
 	(