Expose all files included in PCH/PCM to FileManager.

Else, FileManager will fopen(), Preprocessor will notice that there is a defined
code guard and not enter the source file, thus leaving the file handle unclosed.
Now FileEntry will know that a file comes from a PCh/PCM and not open it when
asking for its stat.

(cherry picked from commit 100b2f3f103467bace9ba2b62cde62f70888db47)

Conflicts:
	interpreter/llvm/src/tools/clang/lib/Serialization/ASTReader.cpp
Split the generation of autoloading maps into parser and fwd declarer.
Adjust pointer gymnastic for signals with no, double, int arguments.
Disable tests until the multiplexing interpreter callback comes.
Avoid to set n arguments to the wrong value if none is present.
This should fix the stressShapes test
Fix header parsing on demand test.
Remove cascaded BaseSelectionRule namespaces (causing compilation failures on Windows)
Add MSVC specific compilation flags
Add MSVC specific compilation flags
Add MSVC specific compilation flags
Add missing include path
Symlinks don't work on Windows, so use copy_directory instead of create_symlink