math: Simplify hypotf implementation

math: Simplify hypotf implementation

Use a more optimized comparison for check for NaN and infinite and
add an inlined issignaling implementation for float.  With gcc it
results in 2 FP comparisons.

The file Copyright is also changed to use  GPL, the implementation was
completely changed by 7c10fd3515f to use double precision instead of
scaling and this change removes all the GET_FLOAT_WORD usage.

Checked on x86_64-linux-gnu.