bfd: Define pagesize variables only for mmap

bfd: Define pagesize variables only for mmap

Define _bfd_pagesize, _bfd_pagesize_m1 and _bfd_minimum_mmap_size only
if HAVE_MMAP is defined.

	* libbfd-in.h (_bfd_pagesize): Declare only if HAVE_MMAP is
	defined.
	(_bfd_pagesize_m1): Likewise.
	(_bfd_minimum_mmap_size): Likewise.
	* libbfd.c (_bfd_pagesize): Define only if HAVE_MMAP is defined.
	(_bfd_pagesize_m1): Likewise.
	(_bfd_minimum_mmap_size): Likewise.
	(bfd_init_pagesize): Likewise.
	* lynx-core.c (lynx_core_file_p): Replace _bfd_pagesize with
	getpagesize.