For C++11, do more checking of initializer lists up-front, enabling some...

For C++11, do more checking of initializer lists up-front, enabling some subset of the final functionality. C just leaves the function early. C++98 runs through the same code path, but has no changed functionality either.
This is a first baby step towards supporting generalized initializer lists. This also removes an aggregate
test case that was just plain wrong, assuming that non-aggregates couldn't be initialized with initializer lists
in C++11 mode.

llvm-svn: 135177