a "loaded" location of the precompiled preamble.
Instead, handle specially locations of preprocessed entities:
-When looking up for preprocessed entities, map main file locations inside the
preamble range to a preamble loaded location.
-When getting the source range of a preprocessing cursor, map preamble loaded
locations back to main file locations.
Fixes rdar://10175093 & http://llvm.org/PR10999
llvm-svn: 140519