re PR middle-end/29335 (transcendental functions with constant arguments should be resolved at compile-time)

	PR middle-end/29335
	* builtins.c (fold_builtin_sin, fold_builtin_cos,
	fold_builtin_tan): Fold all constant arguments.  Take a "type"
	argument as necessary.
	(do_mpfr_arg1): New.
	* real.c, real.h (real_from_mpfr, mpfr_from_real): New.

From-SVN: r117983