[Ada] Misplace of internal master renaming declaration

[Ada] Misplace of internal master renaming declaration

gcc/ada/

	* exp_ch3.adb (Expand_N_Full_Type_Declaration): Ensure a _master
	declaration on limited types that might have tasks.
	* exp_ch9.adb (Build_Master_Renaming): For private types, if we
	are processing declarations in the private part, ensure that
	master is inserted before its full declaration; otherwise the
	master renaming may be inserted in the public part of the
	package (and hence before the declaration of its _master
	variable).