powerpc: Fix -fstack-clash-protection -mprefixed-addr ICE [PR93122]

powerpc: Fix -fstack-clash-protection -mprefixed-addr ICE [PR93122]

As mentioned in the PR, the following testcase ICEs because rs, while valid
add_operand is not valid add_cint_operand and so gen_add3_insn fails,
because it doesn't meet the expander predicates.

Here is what I meant as the alternative, i.e. don't check any predicates,
just gen_add3_insn, if that fails, force rs into register and retry.
And, add REG_FRAME_RELATED_EXPR note always when we haven't emitted a single
insn that has rtl exactly matching what we'd add the REG_FRAME_RELATED_EXPR
with (in that case, dwarf2cfi.c is able to figure it out by itself, no need
to waste compile time memory).

2020-02-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/93122
	* config/rs6000/rs6000-logue.c
	(rs6000_emit_probe_stack_range_stack_clash): Always use gen_add3_insn,
	if it fails, move rs into end_addr and retry.  Add
	REG_FRAME_RELATED_EXPR note whenever it returns more than one insn or
	the insn pattern doesn't describe well what exactly happens to
	dwarf2cfi.c.

	* gcc.target/powerpc/pr93122.c: New test.