[Bug c/88088] -Wtrampolines should be enabled by -Wall (or -Wextra)

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88088

--- Comment #16 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Something as trivial as this

===
void h(int (*)(void));
void f(int x)
{
        int g(void) { return x; }
        h(g);
}
===

will already do.  *Anything* that needs trampolines will do.