simplify-rtx: Fix up simplify_logical_relational_operation for vector IOR [PR101008]

simplify_relational_operation callees typically return just const0_rtx
or const_true_rtx and then simplify_relational_operation attempts to fix
that up if the comparison result has vector mode, or floating mode,
or punt if it has scalar mode and vector mode operands (it doesn't know how
exactly to deal with the scalar masks).
But, simplify_logical_relational_operation has a special case, where
it attempts to fold (x < y) | (x >= y) etc. and if it determines it is
always true, it just returns const_true_rtx, without doing the dances that
simplify_relational_operation does.
That results in an ICE on the following testcase, where such folding happens
during expansion (of debug stmts into DEBUG_INSNs) and we ICE because
all of sudden a VOIDmode rtx appears where it expects a vector (V4SImode)
rtx.

The following patch fixes that by moving the adjustement into a separate
helper routine and using it from both simplify_relational_operation and
simplify_logical_relational_operation.

2021-06-11  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/101008
	* simplify-rtx.c (relational_result): New function.
	(simplify_logical_relational_operation,
	simplify_relational_operation): Use it.

	* gcc.dg/pr101008.c: New test.