bfd_get_size cache

bfd_get_size cache

We have calls to bfd_get_size when swapping in ELF section headers.
Since object files can have a large number of sections, it's worth
caching the file size rather than making lots of stat system calls.

	* bfd.c (struct bfd): Move format and direction to other
	bitfields.  Add "size".
	* bfdio.c (bfd_get_size): Cache size when not writing file.
	* opncls.c (bfd_get_debug_link_info_1): Allow for bfd_get_size
	returning zero, ie. unknown.
	(bfd_get_alt_debug_link_info): Likewise.
	* bfd-in2.h: Regenerate.