lang/cint: Unbreak build with GCC 9
Gcpp_list.cxx: In function 'int Glist_49_0_10(Gvalue*, const char*, Gparam*, int)':
Gcpp_list.cxx:707:109: error: 'std::cxx11::list<int, std::allocator<int> >::iterator' {aka 'struct std::_List_iterator<int>'} has no member named 'operator=='; did you mean 'operator='?
707 | G__letint(result7, 103, (long) ((list<int,allocator<int> >::iterator*) G__getstructoffset())->operator==(*(list<int,allocator<int> >::iterator*) libp->para[0].ref));
| ^~
| operator=Gcpp_list.cxx: In function 'int Glist_49_0_11(Gvalue*, const char*, Gparam*, int)':
Gcpp_list.cxx:713:109: error: 'std::cxx11::list<int, std::allocator<int> >::iterator' {aka 'struct std::_List_iterator<int>'} has no member named 'operator!='; did you mean 'operator='?
713 | G__letint(result7, 103, (long) ((list<int,allocator<int> >::iterator*) G__getstructoffset())->operator!=(*(list<int,allocator<int> >::iterator*) libp->para[0].ref));
| ^~
| operator=While here make the build abort fast on build errors instead of
carrying on like nothing happened.
PR: 238907
Reported by: antoine (via exp-run in PR 238330)