[Darwin] Don't jam symbol stubs on for kernel code.

[Darwin] Don't jam symbol stubs on for kernel code.

For PPC Darwin, we need the JBSR long jump code to be enabled when generating
kernel code.  Now we have that handled in rs6000.c, we can drop the conflated
setting in the common code.  Symbol stubs are not generated for any X86 case.

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

	* config/darwin.c (darwin_override_options): Don't jam symbol stubs
	on for kernel code.

From-SVN: r273180