-ffast-math was added in ff14092d8d0 with a comment that it "helps SINC
resampler to auto-vectorize". The flag is an alias for "-fno-math-errno
-funsafe-math-optimizations -ffp-contract=fast -fno-honor-infinities
-fno-honor-nans". The last two of those cause compiler complaints
because while the flag was meant for this file, it's shared across the
codebase that includes statements that operate on infinities and NaNs.
GCC 13.3 with -fopt-info-vec reports 18 vectorizations for `-O3
-ffast-math`, 17 for `-O3 -fno-math-errno -funsafe-math-optimizations
-ffp-contract=fast` and also 17 for plain `-O3`. So using the subset of
-ffast-math without the offending flags buys nothing and loses 1
vectorization.
Both GCC and Clang provide the "fast-math" pragma directive, which I add
to this one file that benefits from it, under the condition that it's
supported. -ffast-math is removed from most of the makefiles.
