[libclc] Mov erf & erfc to CLC library (#140524)
This completes the set of maths builtins.
No attempt to vectorize or optimize this code. The implementation is
licensed to SunPro so will probably need to be replaced at some point in
the future anyway. Calls to other builtins have been replaced with the
CLC equivalents, and some bit-hacking was replaced with the fabs
builtin.
