[Darwin] Make a final check on PIC options.

[Darwin] Make a final check on PIC options.

Final check on PCI options; for Darwin these are not dependent on the PIE
ones, although PIE does require PIC to support it.  Specifically, for Darwin,
"fPIC fno-PIE" should result in the same as "-fno-PIE -fPIC".

2019-07-07  Iain Sandoe  <iain@sandoe.co.uk>

	* config/darwin.c (darwin_override_options): Make a final check on PIC
	options.

From-SVN: r273181