ggml : prevent builds with -ffinite-math-only (llama/7726)

ggml : prevent builds with -ffinite-math-only (llama/7726)

This enforces a check that -fno-finite-math-only was set and that the operating
compiling mode is not in finite maths mode. This is because during rewriting of
silu and softmax for cpu #7154 there emerged an issue where the result that was
observed when >1 slot was nondeterministic as found by @JohannesGaessler.

@LostRuins narrowed the problem down to -ffinite-math-only which was theorised
to be due to SiLU, instead of flushing small values to 0, returns NaN or some
other garbage. @jart proposed a fix that @ggerganov then implemented in this fix

ref https://github.com/ggerganov/llama.cpp/pull/7154#issuecomment-2145661825