Fix PR1992 by computing the right type for string literals, which

Fix PR1992 by computing the right type for string literals, which
is an array type not a pointer type.  This requires updating some
diags that change and updating the code generator to handle the
proper form of strings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@46941 91177308-0d34-0410-b5e6-96231b3b80d8