[Ada] Freeze target type on qualified expression expansion

[Ada] Freeze target type on qualified expression expansion

An object declaration (other than a deferred constant declaration)
causes freezing where it occurs (13.14(6)), which means every name
occurring within it causes freezing (13.14(4/1)), and when the name in a
subtype_mark causes freezing, the denoted subtype is frozen (13.14(11)).
Hence, one needs to freeze the target type when expanding a qualified
expression.

gcc/ada/

	* exp_ch4.adb (Expand_N_Qualified_Expression): Freeze
	Target_Type.