ada: Fix wrong initialization of library-level object by conditional expression

The previous fix was not robust enough in the presence of transient scopes.

gcc/ada/ChangeLog:

	* exp_ch4.adb (Insert_Conditional_Object_Declaration): Deal with a
	transient scope being created around the declaration.
	* freeze.adb (Freeze_Entity): Do not call Freeze_Static_Object for
	a renaming declaration.