* libc/time/gmtime_r.c (gmtime_r): Fixed bug in calculations for dates
	after year 2069 or before year 1901. Ideas for solution taken from
	musl's __secs_to_tm()
	* libc/machine/aarch64/strrchr.S: New file.
	* libc/machine/aarch64/strrchr-stub.c: New file.
	* libc/machine/aarch64/Makefile.am: Add them to build list.
	* libc/machine/aarch64/Makefile.in: Regenerated.