[clang] [llvm] Fix c-index-test when compiling llvm to a dylib (PR #219092)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

To clarify the problem that I found: if you build as a dylib the c-index-test crash tests hang as the test results in a dead thread holding a lock, but because it's a dylib we try to run the destructor for the offline bundler's TimerGroup, which blocks because the lock is held by the dead thread.

https://github.com/llvm/llvm-project/pull/219092