Resolve conflicts for functions introduced in Android API level 35.
Reported by Po Lu <luangruo@yahoo.com> in
<https://lists.gnu.org/archive/html/bug-gnulib/2024-09/msg00024.html>.
* lib/time.in.h (timezone_t, tzalloc, tzfree): Don't require _GNU_SOURCE
to be defined. Define depending on HAVE_TZALLOC, not HAVE_TIMEZONE_T.
(localtime_rz, mktime_z): Likewise. Override if REPLACE_LOCALTIME_RZ or
REPLACE_MKTIME_Z is 1, respectively.
* lib/time_rz.c: If NEED_TIMEZONE_NULL_SUPPORT, define only localtime_rz
and mktime_z and only as wrappers around the system function.
* m4/time_h.m4 (gl_TIME_H_DEFAULTS): Initialize HAVE_TZALLOC,
REPLACE_LOCALTIME_RZ, REPLACE_MKTIME_Z.
* m4/time_rz.m4 (gl_TIME_RZ): Conditionally set HAVE_TZALLOC,
REPLACE_LOCALTIME_RZ, REPLACE_MKTIME_Z. Conditionally define
NEED_TIMEZONE_NULL_SUPPORT.
* modules/time-h (Makefile.am): Substitute HAVE_TZALLOC,
REPLACE_LOCALTIME_RZ, REPLACE_MKTIME_Z.
* modules/time_rz (Depends-on, configure.ac): Consider HAVE_TZALLOC,
REPLACE_LOCALTIME_RZ, REPLACE_MKTIME_Z. Ignore HAVE_TIMEZONE_T.