Finished semantic analysis of non-type template arguments, to check

Finished semantic analysis of non-type template arguments, to check
for non-external names whose address becomes the template
argument. This completes C++ [temp.arg.nontype]p1.

Note that our interpretation of C++ [temp.arg.nontype]p1b3 differs
from EDG's interpretation (we're stricter, and GCC agrees with
us). They're opening a core issue about the matter.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@64317 91177308-0d34-0410-b5e6-96231b3b80d8