Fix hidden-redecls.m test for some environments

This test was failing in our CI environment, because Jenkins mounts the workspaces into Docker containers using their full path, i.e. /home/jenkins/workspaces/llvm-build.
We've seen permission denied errors because /home/jenkins is mounted with root permissions and the default cache directory under Linux is $HOME/.cache.

The fix is to explicitly provide the -fmodules-cache-path, which the other tests already seem to provide.

Reviewed By: akyrtzi

Differential Revision: https://reviews.llvm.org/D89453