Revert "[modules][cxxmodules] Switch back to umbrella headers."
Revert "[modules][cxxmodules] Switch back to umbrella headers."

This reverts commit 30f04654afc15181503855d565fbe9dc29a7403e.

This breaks when we have OpenGL disabled.

olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,karies/root,karies/root,karies/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root