[Darwin, testsuite] Adjust two tests that fail on newer OS versions.

[Darwin, testsuite] Adjust two tests that fail on newer OS versions.

Newer OS versions (10.14+) do not provide some of the CRTs that are used
for older ones (e.g. 10.5), and thus link tests that specify targeting
such a revision fail. We retain the testing of the correct defined OS
version number but switch to compile-only testing for these two tests.

2019-09-13  Iain Sandoe  <iain@sandoe.co.uk>

	Backport from mainline.
	2019-06-13  Iain Sandoe  <iain@sandoe.co.uk>

	* gcc.dg/darwin-minversion-1.c: Use compile rather than link/run.

From-SVN: r275705