Fix a little thinko in r226017 - the code to actually add the demangled name...

Fix a little thinko in r226017 - the code to actually add the demangled name to the Mangled object got 
moved into the #else branch of the #if/#elif/#endif, so it wasn't getting done in the #if case anymore.

Keep the code to add the demangled name outside of the #if, and then just free the demangled_name
and set it back to NULL in the Windows case.

<rdar://problem/19479499>

llvm-svn: 226088