[Bug target/104208] -mlong-double-64 should override a previous -mabi=ibmlongdouble

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104208

--- Comment #11 from Peter Bergner <bergner at gcc dot gnu.org> ---
I tested GCC 11 and it fails the same way, so we'll need to backport this fix
there.