[Bug target/68934] [ARM] using simd types should be rejected if not fpu=neon

["rearnsha at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68934

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Realistically, this is never going to be feasible.  How would you expect the
compiler to distinguish between

#pragma GCC target ("fpu=neon")
typedef ... _some_simd_type;
typedef ... _some_nonsimd_type;

#pragma GCC target ("fpu=vfp")

_some_simd_type this_shouldnt_work;
_some_nonsimd_type this_should_work;

There's no practical way for the compiler to ever know which types should go
out of scope when the target attributes change.

Real code does not scope simd type definitions tightly enough to make this
feasible even if it were desirable.