[x86] AVX FP compare builtins should require AVX target feature (PR28112)

This is a fix for PR28112:
https://llvm.org/bugs/show_bug.cgi?id=28112

The FP comparison intrinsics that take an immediate parameter (rather than specifying
a comparison predicate in the function name) were added with AVX; these are macros in
avxintrin.h. This patch makes clang behavior match gcc (error if a program tries to use 
these without -mavx) and matches the Intel documentation, eg:
VCMPPS: m128 _mm_cmp_ps(m128 a, __m128 b, const int imm)

'V' means this is intended to only work with the AVX form of the instruction.

Differential Revision: http://reviews.llvm.org/D21306

llvm-svn: 273311