[msan] add strip_path_prefix flag; print error summary; don't crash while printing summary if debug info is missing. The tests will follow later once we establish the lit-like tests for msan. 

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@174595 91177308-0d34-0410-b5e6-96231b3b80d8