ada: Implement RM 4.5.7(10/3) name resolution rule

ada: Implement RM 4.5.7(10/3) name resolution rule

This rule deals with the specific case of a conditional expression that is
the operand of a type conversion and effectively distributes the conversion
to the dependent expressions with the help of the dynamic semantics.

gcc/ada/

	* sem_ch4.adb (Analyze_Case_Expression): Compute the
	interpretations of the expression only at the end of the analysis,
	but skip doing it if it is the operand of a type conversion.
	(Analyze_If_Expression): Likewise.
	* sem_res.adb (Resolve): Deal specially with conditional
	expression that is the operand of a type conversion.
	(Resolve_Dependent_Expression): New procedure.
	(Resolve_Case_Expression): Call Resolve_Dependent_Expression.
	(Resolve_If_Expression): Likewise.
	(Resolve_If_Expression.Apply_Check): Take result type as
	parameter.
	(Resolve_Type_Conversion): Do not warn about a redundant
	conversion when the operand is a conditional expression.