3c745639bb
To use C++ modules during runtime we need to generate a modulemap and install it alongside the ROOT headers. However, right now we need to turn on cxxmodules to generate a modulemap, which would force experiments to fulfill all the depndencies that cxxmodules brings with it (that is, a modern clang that can build ROOT with C++ modules). This patch untangles the modulemap generation from the cxxmodules option, so that we always generate a modulemap even when cxxmodules is turned off. We now also install the modulemap alongside the ROOT headers. No functional change for normal ROOT expected here, as the modulemap will just be ignored without having runtime C++ modules enabled.