Draft: Add emulation of fused MACs
At VFPv4 the family of VFMA/VFMS/VFNMA/VFNMS instructions were added which are very handy for implementing polynomials in transcendental functions without multiple roundings at each step. In order to allow a common implementation of transcendentals to cover all machines RISC OS runs on with VFP, emulate them when not available.
The implementation comes from OpenLibm.
There's a test bed in Test/FMA does both timing tests and checks that the results are bit identical to ARM's instruction. For that to make sense clearly it needs to be run on something with VFPv4 otherwise it's comparing itself with itself!