Introduce SourceManager::PredefinesFileID, to allow each checking of whether
a source location came from the predefines buffer.
For ModuleLoader::makeModuleVisible() also pass the source location where the
module import occurred.
[modules] Introduce ModuleFile::DirectImportLoc which is the source location
where the module was explicitly or implicitly imported in the local translation unit.
Replace LDriu*[bhdw]_indexed_V4 instructions with "def Pats".
libclang: add comments for CXStringFlag