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

[mark at gcc dot gnu.org]

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

--- Comment #4 from Mark Wielaard <mark at gcc dot gnu.org> ---
I think the point of the warning is to note that executable code is generated
on the stack (which seems to always be something to warn about IMHO).

But I am fine with only enabling -Wtrampolines with -Wall for targets that 
explicitly need an executable stack for that. What is the correct way to detect
the target needs that?