The new routines operate on the built-in enum rather than on tree decls.
The idea is to extend this to handle internal functions too, with a
combined enum for both.

The patch also moves fold_fma too, with the same prototype.  The long-term
plan is to replace FMA_EXPR with an internal function, for consistency
with the way that things like SQRT will be handled.

Tested on x86_64-linux-gnu, arm-linux-gnueabi and aarch64-linux-gnu.

gcc/
	* builtins.h (fold_fma): Move to fold-const-call.h.
	* builtins.c: Include fold-const-call.h.
	(mathfn_built_in_2): New function, split out from...
	(mathfn_built_in_1): ...here.
	(do_real_to_int_conversion, fold_const_builtin_pow)
	(fold_const_builtin_logb, fold_const_builtin_significand)
	(fold_const_builtin_load_exponent, do_mpfr_arg1, do_mpfr_arg2)
	(do_mpfr_arg3, do_mpfr_sincos, do_mpfr_bessel_n, do_mpc_arg1): Delete.
	(fold_builtin_sincos): Use fold_const_call to handle constants.
	(fold_builtin_1, fold_builtin_2, fold_builtin_3): Add explicit
	checks for ERROR_MARK.  Use fold_const_call to handle constant
	folds for math functions.
	(fold_fma): Move to fold-const-call.c.
	* fold-const.c: Include fold-const-call.h.
	* Makefile.in (OBJS): Add fold-const-call.o.
	(PLUGIN_HEADERS): Add fold-const-call.h.
	* realmpfr.h (real_from_mpfr): Allow the format to be specified
	directly.
	* realmpfr.c (real_from_mpfr): Likewise.
	* fold-const-call.h, fold-const-call.c: New files.

From-SVN: r229669