Move MREMAP_* to bits/mman-shared.h.

The MREMAP_* flags are identical between bits/mman-linux.h and the
hppa bits/mman.h; thus, they should be in bits/mman-shared.h instead
to avoid unnecessary duplication.  This patch moves them there.

Tested for x86_64, and with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/bits/mman-linux.h [__USE_GNU]
	(MREMAP_MAYMOVE): Do not define here.
	[__USE_GNU] (MREMAP_FIXED): Likewise.
	* sysdeps/unix/sysv/linux/bits/mman-shared.h [__USE_GNU]
	(MREMAP_MAYMOVE): Define here instead.
	[__USE_GNU] (MREMAP_FIXED): Likewise.
	* sysdeps/unix/sysv/linux/hppa/bits/mman.h [__USE_GNU]
	(MREMAP_MAYMOVE): Remove.
	[__USE_GNU] (MREMAP_FIXED): Likewise.