filter_implib_symbols

filter_implib_symbols

This tidies filter_implib_symbols implementations, which I noticed
returned unsigned int but took long symbol counts.  While unsigned int
is very likely sufficient, size_t is better.

_bfd_elf_filter_global_symbols is a linker-only function so really
should be moved to elflink.c, but I left it in elf.c as it calls
sym_is_global, a static function in elf.c.

	* elf-bfd.h (struct elf_backend_data): Take size_t symcount
	and return a size_t from elf_backend_filter_implib_symbols.
	(_bfd_elf_filter_implib_symbols): Likewise.  Rename from
	_bfd_elf_filter_global_symbols.
	* elf.c (_bfd_elf_filter_implib_symbols): Likewise.  Use
	size_t vars too, and avoid unnecessary casts.
	* elf32-arm.c (elf32_arm_filter_cmse_symbols): Likewise.
	(elf32_arm_filter_implib_symbols): Likewise.
	* elflink.c (elf_output_implib): Avoid unneccesary casts.
	Call elf_backend_filter_implib_symbols uncontitionally.
	* elfxx-target.h (elf_backend_filter_implib_symbols): Define
	fallback as _bfd_elf_filter_implib_symbols.