Rework the C strings tests to use ASSERT_SAME_TYPE. NFC there. Also change...

Rework the C strings tests to use ASSERT_SAME_TYPE. NFC there. Also change cwchar.pass.cpp to avoid constructing a couple things from zero - since apparently they can be enums in some weird C library. NFC there, either, since the values were never used.

llvm-svn: 349522