diff: fix timezone bug on Solaris

Problem reported by Vladimir Marek (bug#51228).
* NEWS: Mention this.
* src/context.c (print_context_label): Pass localtz to nstrftime,
instead of always passing 0.
* src/diff.c (main) [!HAVE_TM_GMTOFF]:
Initialize localtz if time_format uses %z.
* src/diff.h (localtz): New decl.
* tests/Makefile.am (TESTS): Add timezone.
* tests/timezone: New test.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/diff.c b/src/diff.c
index fedc7df..0961afb 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -729,6 +729,9 @@ main (int argc, char **argv)
 #else
       time_format = "%Y-%m-%d %H:%M:%S %z";
 #endif
+#if !HAVE_TM_GMTOFF
+      localtz = tzalloc (getenv ("TZ"));
+#endif
     }
   else
     {