Continue RTL verifying in rtl_verify_fallthru

Continue RTL verifying in rtl_verify_fallthru

One case used fatal_insn which does not return which isn't
intended as can be seen by the following erro = 1.  The following
change refactors this to inline the relevant parts of fatal_insn
instead and continue validating the RTL IL.

2021-11-25  Richard Biener  <rguenther@suse.de>

	* cfgrtl.c (rtl_verify_fallthru): Do not stop verifying
	with fatal_insn.
	(skip_insns_after_block): Remove unreachable break and continue.