x86: Use crc32 target option for CRC32 intrinsics

Use crc32 target option for CRC32 intrinsics to support CRC32 intrinsics
without enabling SSE vector instructions.

	* config/i386/i386-c.c (ix86_target_macros_internal): Define
	__CRC32__ for -mcrc32.
	* config/i386/i386-options.c (ix86_option_override_internal):
	Enable crc32 instruction for -msse4.2.
	* config/i386/i386.md (sse4_2_crc32<mode>): Remove TARGET_SSE4_2
	check.
	(sse4_2_crc32di): Likewise.
	* config/i386/ia32intrin.h: Use crc32 target option for CRC32
	intrinsics.