[sanitizer] Change strip_path_prefix flag behavior.

Previously (in tools other than TSan) the entire prefix of the path had to mach
the argument. With this change, only some suffix of the prefix has to match.
This is the same way this flag works in TSan.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@186837 91177308-0d34-0410-b5e6-96231b3b80d8