PR31458, FAIL: MIPS eh-frame 3 with --no-keep-memory

	PR 31458
bfd/
	* elf-bfd.h (_bfd_elf_link_read_relocs),
	(_bfd_elf_link_info_read_relocs): Constify section.
	* elflink.c: Likewise.
	* elfxx-mips.c (_bfd_mips_elf_eh_frame_address_size): Read
	relocs again in case --no-keep-memory.
ld/
	* testsuite/ld-mips-elf/mips-elf.exp: Run --no-keep-memory
	version of eh-frame3 test.