Math Signum optimization for x86

Math.Signum() currently uses two floating point compares and a copy sign operation which involves data movement to gpr and XMM.
It can be optimized to use only one floating point compare and sign computation in XMM. We observe ~25% performance improvement with this optimization.
Base:
Benchmark Mode Cnt Score Error Units
Signum._1_signumFloatTest avgt 5 4.660 ? 0.040 ns/op
 Signum._3_signumDoubleTest avgt 5 4.809 ? 0.043 ns/op
 
Optimized:
signum intrinsic patch
Benchmark Mode Cnt Score Error Units
Signum._1_signumFloatTest avgt 5 3.782 ? 0.019 ns/op
Signum._3_signumDoubleTest avgt 5 3.782 ? 0.017 ns/op