Fix the return types for the SIMD comparisons.
Add a declaration for SIMD.float32x4.select
Remove unnecessary bitcast operators
NaN and -0.0 aware _mm_max_ps and _mm_min_ps

This uses a compare and a select in order to match the x86 semantics
precisely for NaN and -0.0.

This patch also adds the emscripten_float32x4_select function.