This patch is the first step to make module-map-files modular (instead
of requiring a single "module.map"-file per include directory). This
step adds a new "extern module" declaration that enables
module-map-files to reference one another along with a very basic
implementation.
The next steps are:
* Combine this with the use-declaration (from
http://llvm-reviews.chandlerc.com/D1546) in order to only load module
map files required for a specific compilation.
* Add an additional flag to start with a specific module-map-file (instead
of requiring there to be at least one "module.map").
Review: http://llvm-reviews.chandlerc.com/D1637
llvm-svn: 190497
Daniel Jasper