sanitizer_common: Fix the build for platforms that use shared TSDs

Looks like an oversight in 0da172b1

compiler-rt/lib/scudo/scudo_tsd_shared.inc:53:1: error: mutex 'TSD->Mutex' is not held on every path through here [-Werror,-Wthread-safety-analysis]
}
^
compiler-rt/lib/scudo/scudo_tsd_shared.inc:49:12: note: mutex acquired here
  if (TSD->tryLock())
           ^