Update use of raw_fd_ostream, patch by Philip Pfaffe (thanks!)

Fixes PR20846.


git-svn-id: https://llvm.org/svn/llvm-project/poolalloc/trunk@220629 91177308-0d34-0410-b5e6-96231b3b80d8
Fix invalid string comparison due to API change.

This was caught by warnings.

Testcases for behavior in this code would be nice!


git-svn-id: https://llvm.org/svn/llvm-project/poolalloc/trunk@220630 91177308-0d34-0410-b5e6-96231b3b80d8