[Ada] Missing tagged type decoration in corresponding record subtypes

[Ada] Missing tagged type decoration in corresponding record subtypes

The frontend silently skips propagating attribute Is_Tagged_Type to the
constrained corresponding record subtype associated with a protected
type or task type with discriminants. This change does not affect the
functionality of the compiler; it leaves more clean the decoration of
internal entities.

2019-09-17  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* sem_ch3.adb (Constrain_Corresponding_Record): Propagate
	attribute Is_Tagged_Type.

From-SVN: r275777