aarch64: Add a minipass for fusing CC insns [PR88836]

aarch64: Add a minipass for fusing CC insns [PR88836]

This patch adds a small target-specific pass to remove redundant SVE
PTEST instructions.  There are two important uses of this:

- Removing PTESTs after WHILELOs (PR88836).  The original testcase
  no longer exhibits the problem due to more recent optimisations,
  but it can still be seen in simple cases like the one in the patch.
  It also shows up in 450.soplex.

- Removing PTESTs after RDFFRs in ACLE code.

This is just an interim “solution” for GCC 11.  I hope to replace
it with something generic and target-independent for GCC 12.
However, the use cases above are very important for performance,
so I'd rather not leave the bug unfixed for yet another release cycle.

Since the pass is intended to be short-lived, I've not added
a command-line option for it.  The pass can be disabled using
-fdisable-rtl-cc_fusion if necessary.

Although what the pass does is independent of SVE, it's motivated
only by SVE cases and doesn't trigger for any non-SVE test I've seen.
I've therefore gated it on TARGET_SVE and restricted it to PTEST
patterns.

gcc/
	PR target/88836
	* config.gcc (aarch64*-*-*): Add aarch64-cc-fusion.o to extra_objs.
	* Makefile.in (RTL_SSA_H): New variable.
	* config/aarch64/t-aarch64 (aarch64-cc-fusion.o): New rule.
	* config/aarch64/aarch64-protos.h (make_pass_cc_fusion): Declare.
	* config/aarch64/aarch64-passes.def: Add pass_cc_fusion after
	pass_combine.
	* config/aarch64/aarch64-cc-fusion.cc: New file.

gcc/testsuite/
	PR target/88836
	* gcc.target/aarch64/sve/acle/general/ldff1_8.c: New test.
	* gcc.target/aarch64/sve/ptest_1.c: Likewise.