crc: Fix up ICE from optimize_crc_loop [PR120677]

crc: Fix up ICE from optimize_crc_loop [PR120677]

The following testcase ICEs, because optimize_crc_loop inserts a call
statement before labels instead of after labels.

Fixed thusly (plus fixed other issues noticed around it).

2025-06-17  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/120677
	* gimple-crc-optimization.cc (crc_optimization::optimize_crc_loop):
	Insert before gsi_after_labels instead of gsi_start_bb.  Use
	gimple_bb (output_crc) instead of output_crc->bb.  Formatting fix.

	* gcc.c-torture/execute/pr120677.c: New test.