This fixes a typo from 7a795c42ad7f003cd454bf8dbab714714425664c
(https://reviews.llvm.org/D139139). Apparently some codepaths in
that commit weren't actually ever test compiled, since they
can't have worked due to misbalanced parentheses.
Building with Clang (both mingw mode and clang-cl) didn't use
these codepaths, so building in that mode did work.