This was happening because objc_eh_runtime_type wanted to create global 
decls while we were in the middle of processing a function, and 
cp_finish_decl assumed that if we're in a function the decl must belong 
to the function.  We can avoid that assumption by checking the 
DECL_CONTEXT rather than current scope.

Tested x86_64-pc-linux-gnu, applying to trunk.