which will do a binary search and return a pair of iterators
for preprocessed entities in the given source range.

Source ranges of preprocessed entities are stored twice currently in
the PCH/Module file but this will be fixed in a subsequent commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140058 91177308-0d34-0410-b5e6-96231b3b80d8