This is a simplified (and superior) implementation of __invoke, __invokable...

This is a simplified (and superior) implementation of __invoke, __invokable and __invoke_of.  It is superior in that __invoke now handles reference qualified member functions whereas the previous implementation did not.  And it simply has less infrastructure in its implementation.  I'm still learning how to program in C++11 (and probably will be for a long time).  This change does not impact the behavior we're seeing in http://llvm.org/bugs/show_bug.cgi?id=9975

llvm-svn: 131761