Darwin, ppc: Additional change for r12-5974.

This adds a missed change from r12-5974-g926d64906af.
The builin_decls array has been renamed to drop the trailing
_x that was used during the main changes to the builtins.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/ChangeLog:

	* config/rs6000/darwin.h: Drop trailing _x from the
	builtin_decls array name.