[libclc] Move fmin & fmax to CLC library (#134218)
This is an alternative to #128506 which doesn't attempt to change the
codegen for fmin and fmax on their way to the CLC library.
The amdgcn and r600 custom definitions of fmin/fmax are now converted to
custom definitions of __clc_fmin and __clc_fmax.
For simplicity, the CLC library doesn't provide vector/scalar versions
of these builtins. The OpenCL layer wraps those up to the vector/vector
versions.
The only codegen change is that non-standard vector/scalar overloads of
fmin/fmax have been removed. We were currently (accidentally,
presumably) providing overloads with mixed elment types such as
fmin(double2, float), fmax(half4, double), etc. The only vector/scalar
overloads in the OpenCL spec are those with scalars of the same element
type as the vector in the first argument.
