[Bug target/121971] [15/16 Regression] Only warn about musttail on exotic targets?

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121971

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note gcc errors out unlike clang/llvm which will either cause an internal error
(bad) or just not cause a tail call and even produce wrong code in those cases
(worse).