reorg: Do not charge debug insns against search budget [PR127421]

Skip DEBUG_INSNs before decrementing the bounded redundant_insn search
budget.  Debug instructions do not execute and should not hide an otherwise
reachable ordinary redundancy witness.

Assisted-by: OpenAI Codex 5.6 Sol, co-reviewed by Claude and Yongqiang Tian.

	PR rtl-optimization/127421

gcc/ChangeLog:

	* reorg.cc (redundant_insn): Use NONDEBUG_INSN_P in both bounded
	backward walks.  Remove redundant debug-instruction checks.

gcc/testsuite/ChangeLog:

	* gcc.target/sparc/pr127421.c: New test.

Signed-off-by: Yongqiang Tian <yqtian668@gmail.com>