Require fma and f16c for avx512f in std_detect

[sayantn]

The target feature avx512f implies avx2, fma and f16c in rustc, but Intel only guarantees that avx2 will be there when avx512f is present, nothing about fma or f16c. This is correct behavior by rustc, and is based on how the assembler decides what encoding to use, VEX vs EVEX. So this PR simply requires that fma and f16c be present when enabling any AVX512 target features, to match exactly with rustc behavior.

Related:

• Stabilize the avx512 target features rust#138940
• Remove avx512dq and avx512vl implication for avx512fp16 rust#140002
• [X86] Target feature implication mismatch with GCC llvm/llvm-project#136209
• Tracking Issue for AVX512 intrinsics rust#111137

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