darwin, x86, testsuite - Check for an expected error on Darwin.

The test requests an alignment which exceeds the maximum object
file aligment for Darwin, rather than skipping it - test that we
see the expected error.

2019-05-25  Iain Sandoe  <iain@sandoe.co.uk>

	* gcc.target/i386/pr89261.c: Test that the alignment required
	by the test correctly produces the expected error on Darwin.

From-SVN: r271622