This patch implements path::compare according to the current spec. The only observable change is the ordering of "/foo" and "foo", which orders the two paths based on having or not having a root directory (instead of lexically comparing "/" to "foo"). git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@349881 91177308-0d34-0410-b5e6-96231b3b80d8