PR target/106231: Optimize (any_extend:DI (ctz:SI ...)) on x86_64.

PR target/106231: Optimize (any_extend:DI (ctz:SI ...)) on x86_64.

This patch resolves PR target/106231 by providing insns that recognize
(zero_extend:DI (ctz:SI ...)) and (sign_extend:DI (ctz:SI ...)).  The
result of ctz:SI is always between 0 and 32 (or undefined), so
sign_extension is the same as zero_extension, and the result is already
extended in the destination register.

Things are a little complicated, because the existing implementation
of *ctzsi2 handles multiple cases, including false dependencies, which
we continue to support in this patch.

2022-07-18  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR target/106231
	* config/i386/i386.md (*ctzsidi2_<s>ext): New insn_and_split
	to recognize any_extend:DI of ctz:SI which is implicitly extended.
	(*ctzsidi2_<s>ext_falsedep): New define_insn to model a DImode
	extended ctz:SI that has preceding xor to break false dependency.

gcc/testsuite/ChangeLog
	PR target/106231
	* gcc.target/i386/pr106231-1.c: New test case.
	* gcc.target/i386/pr106231-2.c: New test case.