Do not use CXXZeroValueInitExpr for class types. Instead, use

Do not use CXXZeroValueInitExpr for class types. Instead, use
CXXConstructExpr/CXXTemporaryObjectExpr/CXXNewExpr as
appropriate. Fixes PR7556, and provides a slide codegen improvement
when copy-initializing a POD class type from a value-initialized
temporary. Previously, we weren't eliding the copy.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107827 91177308-0d34-0410-b5e6-96231b3b80d8