* builtins.c (fold_builtin_1): Support complex "arc" functions.
	* real.h (HAVE_mpc_arc): Define.

testsuite:
	* gcc.dg/torture/builtin-math-6.c: Test complex "arc" functions.
	* lib/target-supports.exp (check_effective_target_mpc_arc): New.

From-SVN: r152746