Add testing in llvm-lto for ThinLTO caching.

Trying to improve code coverage for `make check`

From: mehdi_amini <mehdi_amini@91177308-0d34-0410-b5e6-96231b3b80d8>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269545 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed