mktime: ease merge of locking code with glibc This shouldn't affect behavior of either Gnulib or glibc. * lib/mktime-internal.h (__libc_lock_lock, __libc_lock_unlock) (__tzset_unlocked) [!_LIBC]: New macros. * lib/mktime.c (tzset) [!_LIBC]: Define this instead of __tzset, if defining either. (__mktime64): Simplify now that mktime-internal defines libc-specific macros to noops when !_LIBC.