re PR middle-end/83654 (-fstack-clash-protection probes below the stack pointer for VLA with constant size)

	PR middle-end/83654
	* explow.c (anti_adjust_stack_and_probe_stack_clash): Test a
	non-constant residual for zero at runtime and avoid probing in
	that case.  Reorganize code for trailing problem to mirror handling
	of the residual.

	PR middle-end/83654
	* gcc.target/i386/stack-check-18.c: New test.
	* gcc.target/i386/stack-check-19.c: New test.

From-SVN: r256182