[Clang][ScanDeps] Change multiple-commands.c test to use -fmodules-cache-path on implicit builds

The module cache escapes the test output dirs in this test. Since its default location maybe
composed of system and user related path this can cause problems in some builders (e.g. not
accessible paths inherited in a chroot environment).

Clean the test a bit by passing `-fmodules-cache-path` inside the test output dirs.

Differential Revision: https://reviews.llvm.org/D133617