Don't use find | xargs in test/Modules/fmodules-validate-once-per-build-session.c

With -fdisable-module-hash, we can implement this with a simple 'cp'.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201231 91177308-0d34-0410-b5e6-96231b3b80d8