[AVX512] Add CHECK-LABELs to test/CodeGen/avx512f-builtins.c
[AVX512] Bring the formatting of avx512fintrin.h closer to avxintrin.h
[AVX512] Reorder functions in avx512fintrin.h

There is no functional change here.

The idea is to have a similar order and categories of functions that we have
in avxintrin.h.
[AVX512] Add FP add/sub/mul intrinsics

Part of <rdar://problem/17688758>
[AVX512] Add non-masking FP store intrinsics

Part of <rdar://problem/17688758>