Darwin, PowerPC, libgcc - Ensure unwinder is built with altivec enabled.

Darwin, PowerPC, libgcc - Ensure unwinder is built with altivec enabled.

When libgcc is built on Darwin, it is usually built for the earliest potential
target (Darwin8, 10.4).  Build for that revision default to assuming that the
processor might be G3 (without vector ops) and there is an outlined function
used for save/restore that checks whether the processor is G3 or G4+ at run-
time.  However, the unwinder itself needs to be built with the assumption of
vector usage so that the relevant outlined functions are called.

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

	* config/rs6000/t-darwin: Ensure that the unwinder is built with
	altivec enabled.

From-SVN: r272017