i386: Implement widen_smul_*_v4si for plain sse2

i386: Implement widen_smul_*_v4si for plain sse2

If we don't implement this pattern, the vectorizer is happy to
unpack the v4si and use the full mulv2di3.  This results in
more element shuffling than is required.

        * config/i386/i386.c (bdesc_args): Update.  Change
        IX86_BUILTIN_VEC_WIDEN_SMUL_ODD_V4SI to OPTION_MASK_ISA_SSE2.
        (IX86_BUILTIN_VEC_WIDEN_SMUL_EVEN_V4SI): New.
        (ix86_builtin_mul_widen_even): Use it.
        (ix86_builtin_mul_widen_odd): Relax SMUL_ODD from sse4 to sse2.
        (ix86_expand_mul_widen_evenodd): Handle signed for sse2.
        * config/i386/sse.md (vec_widen_<s>mult_hi_<V124_AVX2>): Allow
        for all SSE2.
        (vec_widen_<s>mult_lo_<V124_AVX2>): Likewise.
        (vec_widen_<s>mult_odd_<VI4_AVX2>): Likewise.  Relax from V124_AVX2.
        (vec_widen_smult_even_v4si): New.

From-SVN: r189006