[PM] Expose the invalidation API. NFC.

Currently the analysis invalidation API is marked as 'protected', which
means that only the pass itself can invalidate analysis. However, we have
utility functions that should invalidate analysis selectively. Exposing
the invalidation API will allow us to pass the pass to the utility and allow
it to invalidate analysis selectively.

Swift SVN r26459

include/swift/SILPasses/Transforms.h

@@ -103,7 +103,6 @@ namespace swift {
 
     void injectModule(SILModule *Mod) { M = Mod; }
 
-  protected:
     SILModule *getModule() { return M; }
 
     /// Invalidate all of functions in the module, using invalidation