tree-optimization/108691 - remove trigger-happy assert

The following gets rid of the idea that we should prevent setjmp
like calls from popping up in uncontrolled way in the IL for now.
The solution is probably to handle it similar as noreturn has
the ctrl-altering flag on stmts, but use another flag, for example
ctrl-receiving which would also make sure the stmt is first.

	PR tree-optimization/108691
	* tree-ssa-dce.cc (eliminate_unnecessary_stmts): Remove
	assert about calls_setjmp not becoming true when it was false.

	* gcc.dg/pr108691.c: New testcase.