builtins.c (fold_builtin): Constant fold expressions as x*0.5 instead of x/2.0.

builtins.c (fold_builtin): Constant fold expressions as x*0.5 instead of x/2.0.

	* builtins.c (fold_builtin):  Constant fold expressions as x*0.5
	instead of x/2.0.  Optimize sqrt(pow(x,y)) as pow(x,y*0.5),
	log(pow(x,y)) as y*log(x), pow(exp(x),y) as exp(x*y),
	pow(sqrt(x),y) as pow(x,y*0.5) and pow(pow(x,y),z) as pow(x,y*z).
	Delete function scope "fcode" variable to avoid shadowing.

	* gcc.dg/builtins-9.c: New test case.
	* gcc.dg/builtins-10.c: New test case.

From-SVN: r65386