[Bug target/98884] Implement empty struct optimisations on ARM

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98884

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |target
             Target|                            |arm

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
IIRC x86_64 had to change how empty structs are passed, to make C++ consistent
with the x86_64 psABI as used by C (and it wasn't a trivial change to get
right).

If the ARM ABI requires stack space for them then that's unavoidable, but
they're just padding bytes so leaving that stack space uninitialized should be
OK.

Reassigning to the arm target.