Make sure to mark constructors, operator new, and operator delete as

used when we instantiate C++ new expressions, delete expressions, and
object-construction expressions. Fixes PR6424, although we can't test
all of it until we finish implementing lookup of "operator delete" for
new expressions (!).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@97195 91177308-0d34-0410-b5e6-96231b3b80d8