We have an issue where if you use a C function right now that has no...

We have an issue where if you use a C function right now that has no prototype, it isn't marked as extern "C" and the name to lookup is some C++ mangled form of the name.

This used to be the case for "printf" before a function prototype was added to the builtin expression prefix file. This fix makes sure that if we get a mangled name that we don't find in the current target, that we only fall back to looking up function by basename if the function isn't contained in a namespace or class (no decl context).

llvm-svn: 234178