Refactor x86 macros and _ArchTraits

include/ChangeLog:

	* bits/simd_details.h: Remove _GLIBCXX_SIMD_HAVE_* macros.
	(_GLIBCXX_X86): New.
	(__streq_to_1): New.
	(_ArchTraits): Rewrite initialization and reorder feature bits.
	Adjust _M_have_* functions accordingly.
	* bits/simd_mask.h: Use _GLIBCXX_X86 instead of
	_GLIBCXX_SIMD_HAVE_SSE.
	* bits/simd_math.h: Likewise.
	* bits/simd_vec.h: Likewise.
	* bits/simd_x86.h: Likewise.
	* bits/vec_ops.h: Likewise.

Author: mattkretz