aarch64: Stack-clash prologues and VG saves [PR113995]

aarch64: Stack-clash prologues and VG saves [PR113995]

This patch fixes an ICE for a combination of:

- -fstack-clash-protection
- a frame that has SVE save slots
- a frame that has no GPR save slots
- a frame that has a VG save slot

The allocation code was folding the SVE save slot allocation into
the initial frame allocation, so that we had one allocation of
size <size of SVE registers> + 16.  But the VG save code itself
expected the allocations to remain separate, since it wants to
store at a constant offset from SP or FP.

The VG save isn't shrink-wrapped and so acts as a probe of the
initial allocations.  It should therefore be safe to keep separate
allocations in this case.

The scans in locally_streaming_1.c expect no stack clash protection,
so the patch forces that and adds a separate compile-only test for
when protection is enabled.

gcc/
	PR target/113995
	* config/aarch64/aarch64.cc (aarch64_expand_prologue): Don't
	fold the SVE allocation into the initial allocation if the
	initial allocation includes a VG save.

gcc/testsuite/
	PR target/113995
	* gcc.target/aarch64/sme/locally_streaming_1.c: Require
	-fno-stack-clash-protection.
	* gcc.target/aarch64/sme/locally_streaming_1_scp.c: New test.