Still more Doxygen documentation fixes:

Still more Doxygen documentation fixes:
* Escape #, < and @ symbols where Doxygen would try to interpret them;
* Fix several function param documentation where names had got out of sync;
* Delete param documentation referring to parameters that no longer exist.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158472 91177308-0d34-0410-b5e6-96231b3b80d8