ada: Fix loop unnesting issue.

ada: Fix loop unnesting issue.

During loop unnesting, when the loop statements are wrapped in a code
block, the newly created block's scope must be set to the loop
scope (instead of the previous 'Current_Scope' that would point to an
upper scope).

gcc/ada/

	* sem_util.ads (Add_Block_Identifier): Add new extra Scope
	argument.
	* sem_util.adb (Add_Block_Identifier): Likewise and use this scope
	variable instead of Current_Scope.
	* exp_util.adb (Wrap_Statements_In_Block): Add new scope argument
	to Add_Block_Identifier call.