Don't map a file:line:col triplet that is inside the preamble range to

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