[Darwin, PPC] Move the out of line register save/restore to an endfile.

[Darwin, PPC] Move the out of line register save/restore to an endfile.

We have been including this in libgcc, which means that we have to append
-lgcc even when using shared libgcc. In preparation for revision of libgcc
split this into an endfile.

gcc/
2019-06-25  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/darwin.h (ENDFILE_SPEC): New.

libgcc/
2019-06-25  Iain Sandoe  <iain@sandoe.co.uk>

	* config.host: Add libef_ppc.a to the extra files for powerpc-darwin.
	* config/rs6000/t-darwin: (PPC_ENDFILE_SRC, PPC_ENDFILE_OBJS): New.
	Build objects for the out of line save/restore register functions
	so that they can be used for any supported Darwin version.
	* config/t-darwin: Default the build Darwin version to Darwin8
	(MacOS 10.4).

From-SVN: r272659