i386: Correct target attribute for crc32 intrinsics

Complile _mm_crc32_u8/16/32/64 intrinsics with -mcrc32
would meet target specific option mismatch. Correct target pragma
to fix.

gcc/ChangeLog:

	* config/i386/smmintrin.h: Correct target pragma from sse4.1
	and sse4.2 to crc32 for crc32 intrinsics.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/crc32-6.c: Adjust dg-error message.
	* gcc.target/i386/crc32-7.c: New test.