Unrevert r155951, reverted in r155962, with two changes:

 * Work around build failures due to gcc 4.2 bugs.
 * Remove BodyIndexer::TraverseCXXOperatorCallExpr, which was not being called
   prior to this change, and whose presence disables a RecursiveASTVisitor
   stack space optimization after this change.

llvm-svn: 155969