That's my point - GSL is NOT MSVC only, it's a general purpose library and NOT a standard library implementation of a toolchain so any compiler is expected to be able to compile it (it also explicitly targets clang & gcc).
It was originally created by Microsoft and as Herb mentions "all our target platforms", so most likely it gets special treatment.
It was originally created by Microsoft and as Herb mentions "all our target platforms", so most likely it gets special treatment.