[Bug c/93252] Warning for symbols that could be internalized

[trass3r at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93252

--- Comment #2 from Trass3r <trass3r at gmail dot com> ---
Yeah it's in the same vein as the other -Wsuggest warnings which run during
lto.

Like

a.c
void f() {} // can be made static
void g() { f(); }

b.c

void g();
int main() { g(); }