time_r: Add missing declarations on HP-UX 11.

time_r: Add missing declarations on HP-UX 11.

* lib/time.in.h (localtime_r, gmtime_r): Test HAVE_DECL_LOCALTIME_R
instead of HAVE_LOCALTIME_R.
* m4/time_r.m4 (gl_TIME_R): Test whether localtime_r is declared. Set
HAVE_LOCALTIME_R always.
* m4/time_h.m4 (gl_HEADER_TIME_H_DEFAULTS): Initialize
HAVE_DECL_LOCALTIME_R, not HAVE_LOCALTIME_R.
* modules/time (Makefile.am): Substitute HAVE_DECL_LOCALTIME_R, not
HAVE_LOCALTIME_R.
* doc/posix-functions/gmtime_r.texi: Document the HP-UX 11 problem.
* doc/posix-functions/localtime_r.texi: Likewise.