Cache the section contents in x86 check_relocs

Cache the section contents in x86 check_relocs for sections without
TLS relocations.

	* elf32-i386.c (elf_i386_check_tls_transition): Remove abfd.
	Don't check if contents == NULL.
	(elf_i386_tls_transition): Add from_relocate_section.  Check
	from_relocate_section instead of contents != NULL.  Update
	elf_i386_check_tls_transition call.
	(elf_i386_check_relocs): Cache the section contents if
	keep_memory is FALSE.  Pass FALSE as from_relocate_section to
	elf_i386_tls_transition.
	(elf_i386_relocate_section): Pass TRUE as from_relocate_section
	to elf_i386_tls_transition.
	(elf_backend_caches_rawsize): New.
	* elf64-x86-64.c (elf_x86_64_check_tls_transition): Don't check
	if contents == NULL.
	(elf_x86_64_tls_transition): Add from_relocate_section.  Check
	from_relocate_section instead of contents != NULL.
	(elf_x86_64_check_relocs): Cache the section contents if
	keep_memory is FALSE.  Pass FALSE as from_relocate_section to
	elf_x86_64_tls_transition.
	(elf_x86_64_relocate_section): Pass TRUE as from_relocate_section
	to elf_x86_64_tls_transition.
	(elf_backend_caches_rawsize): New.