Corrade/Utility/IntrinsicsSse3.h file new in Git master

Intrinsics for x86 SSE3 instructions.

Equivalent to #include <pmmintrin.h> on most compilers except for GCC 4.8, where it contains an additional workaround to make the instructions available with just the CORRADE_ENABLE_SSE3 function attribute instead of having to specify -msse3 for the whole compilation unit.