Ofast to O3

-Ofast enables -ffast-math, which ignores strict IEEE compliance. This affects the global state for denormal numbers through DAZ (denormals-are-zero) and FTZ (flush-to-zero).
With -fno-protect-parens as well, -Ofast overly aggressively optimizes flops in definitions such as

static FLT X(diff)(FLT x, FLT y) {return x - y;}

resulting in the failure of test_tdc for the past while. It should be possible to reactivate this test now.