Fix the rest of PR9316 along with some other bugs spotted by inspection.

I tried to add test cases for these, but I can't because variables
aren't warned on the way functions are and the codegen layer appears to
use different logic for determining that 'a' and 'g' in the test case
should receive C mangling. I've included the test so that if we ever
switch the codegen layer to use these functions, we won't regress due to
latent bugs.

llvm-svn: 126453