PR target/106877: Robustify reg-stack to malformed asm.

PR target/106877: Robustify reg-stack to malformed asm.

This patch resolves PR target/106877 an ICE-on-invalid inline-asm
regression.  An innocent upstream change means that the test case
from PR inline-asm/84683 now hits a different assert in reg-stack.cc's
move_for_stack_reg.  Fixed by duplicating Jakub's solution to PR 84683
https://gcc.gnu.org/pipermail/gcc-patches/2018-March/495193.html at
this second (similar) gcc_assert.

2022-09-13  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR target/106877
	* reg-stack.cc (move_for_stack_reg): Check for any_malformed_asm
	in gcc_assert.

gcc/testsuite/ChangeLog
	PR target/106877
	* g++.dg/ext/pr106877.C: New test case.