[clangd] Trace time the operations wait on Semaphore.

The Semaphore is currently used to limit the number of concurrently
running tasks. Tracing the wait times will allow to find out how much
time is wasted waiting on other operations to complete.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@334495 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed