Un-revert "[Option] Fix PR37006 prefix choice in findNearest"

Summary:
In https://reviews.llvm.org/rL332804 I loosed the assertion in
the Clang driver test that forced me to revert
https://reviews.llvm.org/rL332299. Once this lands I should be
able to narrow down what caused PS4 buildbots to fail, and
reinstate the check in that test.

Test Plan: check-llvm & check-clang



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332805 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed