* fold-const.c (omit_one_operand): No longer static.
	* tree.h (omit_one_operand): Prototype here.
	(div_and_round_double): Keep fold-const.c prototypes together.
	* builtins.c (builtin_mathfn_code): Handle binary built-in
	funtions, such as "pow" and "atan2".
	(fold_builtin): Optimize both pow(x,0.0) and pow(1.0,y) to 1.0.
	Simplify optimizations using "type" the builtin's return type.

	* gcc.dg/builtins-5.c: New test case.

From-SVN: r63273