tree-vrp.c (compare_name_with_value): Always set used_strict_overflow if we get a result from the variable itself.

./:	* tree-vrp.c (compare_name_with_value): Always set
	used_strict_overflow if we get a result from the variable itself.
testsuite/:
	* gcc.dg/Wstrict-overflow-17.c: New test.

From-SVN: r125269