C11 compiler selection?

[Michael Dickens]

Do we have a portgroup or whatever to select a compiler for c11 compliance? In my testing using the c++11 1.1 PG isn't sufficient ... which might mean that the c++11 compiler compliance selection isn't correct (but I doubt it); or that c11 compiler compliance selection is different that that for c++11 (which is my guess). In a quick search I can find nothing obvious to do this in MP. Thanks for your thoughts / insights! - MLD  (ps> I need this for the latest GLFW-devel, which uses <stdatomic.h> ...)