arm: correctly handle negating INT_MIN in arm_split_atomic_op [PR97534]

arm: correctly handle negating INT_MIN in arm_split_atomic_op [PR97534]

arm_split_atomic_op handles subtracting a constant by converting it
into addition of the negated constant.  But if the type of the operand
is int and the constant is -1 we currently end up generating invalid
RTL which can lead to an abort later on.

The problem is that in a HOST_WIDE_INT, INT_MIN is represented as
0xffffffff80000000 and the negation of this is 0x0000000080000000, but
that's not a valid constant for use in SImode operations.

The fix is straight-forward which is to use gen_int_mode rather than
simply GEN_INT.  This knows how to correctly sign-extend the negated
constant when this is needed.

gcc/
	PR target/97534
	* config/arm/arm.c (arm_split_atomic_op): Use gen_int_mode when
	negating a const_int.
gcc/testsuite
	* gcc.dg/pr97534.c: New test.