To workaround gcc/egcs bugs re: handling of non-toplevel "extern" decls,
lift them out to the top. i.e., extend mechanism by which "typedefs"
are lifted out to the toplevel (for the same reasons) to also encompass
"extern"s.

Note: the default is not to emit an "extern" decl for every _ccall_,
as this runs the chance of (trivially) conflicting with header file
includes. So, to enable, use -optC-femit-extern-decls.