tsan: fix clang warning:
comparison of unsigned expression >= 0 is always true



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@210346 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: flush metamap per-thread cache when thread finishes



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@210347 91177308-0d34-0410-b5e6-96231b3b80d8