ada: Avoid expanding LHS assignments for controlled types

ada: Avoid expanding LHS assignments for controlled types

Expanding a function call that returns a controlled type
on the left-hand side of an assignment should be avoided.
Otherwise we will miss the diagnostic for
trying to assign something to a non-variable element.

gcc/ada/ChangeLog:

	* exp_ch6.adb (Expand_Ctrl_Function_Call): Avoid expansion
	of controlled types when the LHS is a function call.