[ModuleMap][CrashReproducer] Collect headers from inner frameworks

(1) Collect headers under inner frameworks (frameworks inside other
other frameworks).
(2) Make sure we also collect the right header files inside them.

More info on (2):

Consider a dummy framework module B, with header Frameworks/B/B.h. Now
consider that another framework A, with header Frameworks/A/A.h, has a
layout with a inner framework Frameworks/A/Frameworks/B/B.h, where the
"B/B.h" part is a symlink for Frameworks/B/B.h. Also assume that
Frameworks/A/A.h includes <B/B.h>.

When parsing header Frameworks/A/A.h, framework module lookup is
performed in search for B, and it happens that
"Frameworks/A/Frameworks/B/B.h" path is registered in the module instead
of real "Frameworks/B/B.h". This occurs because
"Frameworks/A/Frameworks/B/B.h" is scanned first by the FileManager,
when looking for inner framework modules under Frameworks/A/Frameworks.
This makes Frameworks/A/Frameworks/B/B.h the default cached named inside
the FileManager for the B.h file UID.

This leads to modules being built without consistent paths to underlying
header files. This is usually not a problem in regular compilation flow,
but it's an issue when running the crash reproducer. The issue is that
clangs collect "Frameworks/A/Frameworks/B/B.h" but not
"Frameworks/B/B.h" into the VFS, leading to err_mmap_umbrella_clash. So
make sure we also collect the original header.

Differential Revision: http://reviews.llvm.org/D20194

rdar://problem/25880368

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@269502 91177308-0d34-0410-b5e6-96231b3b80d8