These tests were creating a modules.idx file in my clang checkout, not
the build directory or temp.

All the other tests in this directory use -fmodules-cache-path=%t so
updated these to match.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@243657 91177308-0d34-0410-b5e6-96231b3b80d8