ada: Add Global contracts to Ada.Numerics.Generic_Elementary_Functions

ada: Add Global contracts to Ada.Numerics.Generic_Elementary_Functions

GNATprove raised warnings about unspecified Global contracts when
using functions from an instance of
Ada.Numerics.Generic_Elementary_Functions. This patch adds null Global
contracts to all subprograms.

gcc/ada/

	* libgnat/a-ngelfu.ads (Sqrt): Add Global contracts.
	(Log): Likewise.
	(Exp): Likewise.
	("**"): Likewise.
	(Sin): Likewise.
	(Cos): Likewise.
	(Tan): Likewise.
	(Cot): Likewise.
	(Arcsin): Likewise.
	(Arccos): Likewise.
	(Arctan): Likewise.
	(Arccot): Likewise.
	(Sinh): Likewise.
	(Cosh): Likewise.
	(Tanh): Likewise.
	(Coth): Likewise.
	(Arcsinh): Likewise.
	(Arccosh): Likewise.
	(Arctanh): Likewise.
	(Arccoth): Likewise.