[sanitizer] A low-level vector implementation to be used in leak checking code. Patch by Sergey Matveev

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176089 91177308-0d34-0410-b5e6-96231b3b80d8
[Sanitizer] Don't die if external symbolizer is used on Mac, where it's not implemented yet

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176091 91177308-0d34-0410-b5e6-96231b3b80d8