We should consider splitting Clang and Apple Clang into separate compilers, like %clang and %apple.

Rationale

I'm trying to build the latest version of scikit-learn, which recently added an OpenMP dependency. Apple Clang currently does not come with OpenMP support by default, so I need to add a dependency on llvm-openmp. However, there is currently no way to check whether Clang or Apple Clang are in use via the spec.

Several other packages need to know whether we are using Clang or Apple Clang:

• fftw
• hpgmg
• libceed
• m4
• openblas
• py-scikit-learn
• qt
• sundials
• valgrind
• vtk
• xios
• yaml-cpp

Description

The only current workaround is to use the following spec:

when='%clang platform=darwin'

However, this does not work if you install Clang yourself on macOS.

@davydden