ada: Add support for No_Implicit_Conditionals to nonbinary modular types

ada: Add support for No_Implicit_Conditionals to nonbinary modular types

The expansion of additive operations for nonbinary modular types implemented
in the front-end and its counterpart in code generators may create branches,
which is not allowed when restriction No_Implicit_Conditionals is in effect.

This changes it to use an explicit Mod operation when the restriction is in
effect, which is assumed not to create such branches.

gcc/ada/

	* exp_ch4.adb (Expand_Nonbinary_Modular_Op): Create an explicit Mod
	for additive operations if No_Implicit_Conditionals is in effect.
	(Expand_Modular_Addition): Likewise.
	(Expand_Modular_Subtraction): Likewise.
	(Expand_Modular_Op): Always use an unsigned type obtained by calling
	Small_Integer_Type_For on the required size.