Fix build with llvm trunk.

commit 8c968628473c7de416e3f468fead20023f33107e
Author: Rafael Espindola <rafael.espindola@gmail.com>
Date:   Mon Aug 25 18:16:47 2014 +0000

    Modernize raw_fd_ostream's constructor a bit.

    Take a StringRef instead of a "const char *".
    Take a "std::error_code &" instead of a "std::string &" for error.

    A create static method would be even better, but this patch is already a bit too
    big.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216393 91177308-0d34-0410-b5e6-96231b3b80d8

commit 1a7f705fba4b387ad251b0f303acec5c7131971d
Author: Rafael Espindola <rafael.espindola@gmail.com>
Date:   Wed Aug 27 20:03:13 2014 +0000

    Return a std::unique_ptr when creating a new MemoryBuffer.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216583 91177308-0d34-0410-b5e6-96231b3b80d8