tsan: allow a front-end to provide default suppressions


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173345 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: suppress reports using both stacks


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173346 91177308-0d34-0410-b5e6-96231b3b80d8