intended for debugging and diagnostic output), just inspect the spelling
to check for specific prefixes in drectve section flags.

In addition to being significantly cheaper and not relying on
a debugging interface, this also avoids creating a temporary string and
binding it to StringRef variable. We then went on to access it after the
memory had been deallocated.

This bug too was caught by ASan. I love ASan so much. =]

llvm-svn: 193487