Fix two test failures caused by Windows mangling of function types.

On Windows the function template `template <class T> void test()` has
the same mangled name when instantiated with the distinct types `void()`
and `void() noexcept`. When this occurs Clang emits an error. This error
was causing two type-traits tests to fail.

However this can be worked around by using class templates instead of
function templates, which is what this patch does to fix the errors.

llvm-svn: 302380