[Bug c++/60304] Including disables -Wconversion-null

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60304

--- Comment #17 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #16)
> A testcase:

==> sys.h <==
#pragma GCC system_header
#if defined false
#undef false
#endif
#define false false


==> nonsys.h <==
#if defined false
#undef false
#endif
#define false false


==> false.c <==
#include "sys.h"
int * foo() {return false;}
#include "nonsys.h"
int * bar() {return false;}