[Ada] Adding assertions on extra formals for BIP function calls

[Ada] Adding assertions on extra formals for BIP function calls

This patch adds assertions to ensure that the frontend passes to the
backend the right number of extra parameters required for build in place
function calls. No functional change.

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

gcc/ada/

	* exp_ch6.ads (Needs_BIP_Task_Actuals): New subprogram.
	* exp_ch6.adb (Add_Task_Actuals_To_Build_In_Place_Call): Code
	cleanup.
	(Check_Number_Of_Actuals): New subprogram.
	(Make_Build_In_Place_Call_In_Allocator): Adding assertion.
	(Make_Build_In_Place_Call_In_Anonymous_Context): Adding
	assertion.
	(Make_Build_In_Place_Call_In_Assignment): Adding assertion.
	(Make_Build_In_Place_Call_In_Object_Declaration): Code cleanup
	plus assertion addition.
	(Needs_BIP_Task_Actuals): New subprogram.
	* sem_ch6.adb (Create_Extra_Formals): Rely on
	Needs_BIP_Task_Actuals() to check if the master of the tasks to
	be created, and the caller's activation chain formals are
	needed.

From-SVN: r275772