Update bits/mman.h constants and tst-mman-consts.py for Linux 5.3.

The Linux 5.3 uapi headers have some rearrangement relating to MAP_*
constants, which includes the effect of adding definitions of MAP_SYNC
on powerpc and sparc.  This patch updates the corresponding glibc
bits/mman.h headers accordingly, and updates the Linux kernel version
number in tst-mman-consts.py to reflect that these constants are now
current with that kernel version.

Tested with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/powerpc/bits/mman.h [__USE_MISC]
	(MAP_SYNC): New macro.
	* sysdeps/unix/sysv/linux/sparc/bits/mman.h [__USE_MISC]
	(MAP_SYNC): Likewise.
	* sysdeps/unix/sysv/linux/tst-mman-consts.py (main): Update Linux
	kernel version number to 5.3.