Add dependencies from imported modules with -MD

Add module dependencies to the dependency files created by -MD/-MMD/etc.
by attaching an ASTReaderListener that will call into the dependency
file generator when a module input file is seen in the serialized AST.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203208 91177308-0d34-0410-b5e6-96231b3b80d8