Set CPU type in BFD backend for x86_64-nacl* and i?86-nacl* targets

bfd/
	* archures.c (bfd_mach_i386_nacl): Fix definition so it doesn't
	collide with bfd_mach_l1om.
	* bfd-in2.h: Regenerate.

	* elf32-i386.c (elf32_i386_nacl_elf_object_p): New function.
	(elf_backend_object_p): Use that in elf32-i386-nacl definition.
	* elf64-x86-64.c (elf64_x86_64_nacl_elf_object_p): New function.
	(elf_backend_object_p): Use that in elf64-x86-64-nacl definition.
	(elf32_x86_64_nacl_elf_object_p): New function.
	(elf_backend_object_p): Use that in elf32-x86-64-nacl definition.

binutils/
	* objdump.c (dump_dwarf): Grok bfd_mach_x86_64_nacl and
	bfd_mach_x64_32_nacl as equivalent to bfd_mach_x86_64.

ld/testsuite/
	* ld-x86-64/x86-64.exp (mixed1, mixed2): Loosen error string match
	so it accepts "i386:nacl" in place of "i386".
	* ld-x86-64/ilp32-2.d: Likewise.
	* ld-x86-64/ilp32-3.d: Likewise.
	* ld-x86-64/lp64-2.d: Likewise.
	* ld-x86-64/lp64-3.d: Likewise.

(cherry picked from commit 64b384e1e821cedccefa24f6d5bb82d353546ca1)
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