[Sanitizer] support running external llvm-symbolizer on Mac

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@183730 91177308-0d34-0410-b5e6-96231b3b80d8
[Sanitizer] add file forgotten in r183730

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@183732 91177308-0d34-0410-b5e6-96231b3b80d8