Use SSE intrinsics instead of GCC specific __builtin functions

The __builtin_ia32_loadups and __builtin_ia32_storeups functions are GCC
specific and are not supported by compilers like LLVM. Instead use the more
often supported SSE intrinsics.
Merge pull request #2 from ecsv/llvm

Use SSE intrinsics instead of GCC specific __builtin functions