re PR target/54160 (gcc should not define __OBJC2__ when lang is not set to ObjC (gcc 4.6 and later))

	PR target/54160
	* config/t-darwin (darwin-c.o): Depend on $(CPP_INTERNAL_H).
	* config/darwin-c.c (darwin_cpp_builtins): Only set __OBJC2__
	when in obj mode.
	Include libcpp/internal.h.

From-SVN: r194227