Be more careful about updating the failed-modules set

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172035 91177308-0d34-0410-b5e6-96231b3b80d8
clang-c/Index.h: Clarify empty argument with (void) for C89.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172037 91177308-0d34-0410-b5e6-96231b3b80d8