arm: temporarily disable 'local' pcs selection (PR96882)

The arm port has an optimization used during selection of the
function's ABI to permit deviation from the strict ABI when the
function does not escape the current translation unit.

Unfortunately, the ABI selection it makes can be unsafe if it changes
how a result is returned because not enough information is available
via the RETURN_IN_MEMORY hook to determine where the function gets
used.  This can result in some parts of the compiler thinking a value
is returned in memory while others think it is returned in registers.

To mitigate this, this patch temporarily disables the optimization and
falls back to using the default ABI for the translation.

gcc/ChangeLog:

	PR target/96882
	* config/arm/arm.cc (arm_get_pcs_model): Disable selection of
	ARM_PCS_AAPCS_LOCAL.