* builtins.c (do_mpc_arg2): New.
	(fold_builtin_2): Fold builtin cpow.
	* real.h (HAVE_mpc_pow): New.

testsuite:
	* gcc.dg/torture/builtin-math-5.c: Add more cases.
	* gcc.dg/torture/builtin-math-6.c: Likewise.  Depend on
	effective target "mpc_pow".
	* lib/target-supports.exp (check_effective_target_mpc_pow): New.

From-SVN: r149716