Collect the modulemaps even if no overlay is set.
Collect the modulemaps even if no overlay is set.

This patch tightens the implementation of the collection of modulemap files.
It still gathers all 'system' modulemaps necessary for cling to run if
-fno-implicit-module-maps is specified.

This patch should unbreak our osx builds.

root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling