Add explicit attributes to mark functions as having had their

CoreFoundation object-transfer properties audited, and add a #pragma
to cause them to be automatically applied to functions in a particular
span of code.  This has to be implemented largely in the preprocessor
because of the requirement that the region be entirely contained in
a single file;  that's hard to impose from the parser without registering
for a ton of callbacks.

llvm-svn: 140846