Replace uses of strncmp with memcmp

Replace uses of strncmp with memcmp

Avoids gcc pr85623 for these calls.

	* cofflink.c (_bfd_coff_link_input_bfd): Use memcmp rather than
	strncmp when checking for ".bf" special symbol.
	* prXXigen.c (_bfd_XXi_swap_scnhdr_out): Make pe_required_section_flags
	section name a char array, remove sentinal known_sections entry,
	and adjust loop over known_sections to suit.  Use memcmp rather
	than strncmp.