Fixed compile errors for AVX2, FMA3 and FMA4 CMake checks.

AVX2 and FMA3 were failing on my Haswell machine due to compile errors in the intrinsics.  These are now correctly detected on my machine with gcc 4.8 and clang 3.4
Merge pull request #12 from khegeman/cmake_simd_fixes

Fixed compile errors for AVX2, FMA3 and FMA4 CMake checks.