[AArch64] big.LITTLE option rewriting bug

gcc/

	* config/aarch64/aarch64-elf.h (ASM_SPEC): Remove identity spec for
	-mcpu.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@206399 138bc75d-0d04-0410-961f-82ee72b054a4