There's something fundamentally broken with CC variables.  Today I tested these easyconfigs by building the Mercurial modules because they depend on everything.  I just checked log files and CC was being set to clang.  But if I now try to rebuild anything, CC gets set to gcc.

Just removed everything except GCC and Clang and tried to build Mercurial with base class order set to 'Clang, Gcc' and I see that CC=clang for OpenBLAS.  While with 'Gcc, Clang' CC=gcc.