maintainer-feedback requested: [Bug 268795] x11/mate-panel: fix build with clang 15

From: <bugzilla-noreply_at_freebsd.org>
Date: Sat, 07 Jan 2023 00:32:06 UTC 
Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-gnome (Nobody)
<gnome@FreeBSD.org> for maintainer-feedback:
Bug 268795: x11/mate-panel: fix build with clang 15
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=268795



--- Description ---
During an exp-run for llvm 15 (see bug 265425), it turned out that
x11/mate-panel failed to build with clang 15:

  clock-location.c:454:22: error: incompatible pointer to integer conversion
assigning to 'glong' (aka 'long') from 'char *(int, int)' [-Wint-conversion]
	  sys_timezone = timezone;
		       ^ ~~~~~~~~
  clock-location.c:462:24: error: incompatible pointer to integer conversion
assigning to 'glong' (aka 'long') from 'char *(int, int)' [-Wint-conversion]
	  local_timezone = timezone;
			 ^ ~~~~~~~~

This is because 'timezone' as a global external variable does not exist on
FreeBSD: it is a glibc-ism. Use struct tm's tm_gmtoff field instead, which has
its sign reversed from the glibc global. There is also no need to manually
account for DST, as tm_gmtoff includes that.