Auto-vectorizer generates 128-bit AVX insns by default for bdver1.

	* config/i386/i386.opt (mprefer-avx128): Redefine the flag as a Mask option.
	* config/i386/i386.h (ix86_tune_indices): Add X86_TUNE_AVX128_OPTIMAL entry.
	(TARGET_AVX128_OPTIMAL): New definition.
	* config/i386/i386.c (initial_ix86_tune_features): Initialize
	X86_TUNE_AVX128_OPTIMAL entry.
	(ix86_option_override_internal): Enable the generation
	of the 128-bit instructions when TARGET_AVX128_OPTIMAL is set.
	(ix86_preferred_simd_mode): Use TARGET_PREFER_AVX128.
	(ix86_autovectorize_vector_sizes): Use TARGET_PREFER_AVX128.

From-SVN: r175661