- Normalize arch string would help the multi-lib handling, e.g. rv64gc and
   rv64g_c are both valid and same arch, but latter one would confuse
   the detection of multi-lib, earlier normalize can resolve this issue.

gcc/ChangeLog:

	* config/riscv/riscv.h (ASM_SPEC): Remove riscv_expand_arch call.
	(DRIVER_SELF_SPECS): New.