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

	PR middle-end/29335
	* builtins.c (do_mpfr_sincos): New.
	(fold_builtin_1): Use it to fold builtin sincos.

testsuite:
	* gcc.dg/torture/builtin-math-3.c: Fix semicolons.
	(TESTIT_2P, TESTIT_2P_R): New macros.  Test sincos.

From-SVN: r118409