The RM 3.9.2(19) clause says that the controlling tag value is statically
determined to be the tag of the tagged type involved.  As a matter of fact,
the call would be made dispatching only as a by-product of the propagation
of the controlling tag value to the tag-indeternminate actuals, but that's
unnecessary and not done in the equivalent case of a procedure call with
both statically tagged and tag-indeternminate actuals.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_disp.adb (Check_Dispatching_Call): Merge the two special cases
	where there are no controlling actuals but tag-indeternminate ones.