When calling an access to a subprogram taking an unconstrained
discriminated record as parameter, we fail to pass the extra constrained
actual parameter, which would lead to spurious or missed discriminant
checks.

At the same time we noticed that GNAT sometimes generates trees of the
form:

  (Field1 => 1, Field2 => 2).Field1

we now recognize these in Sem_Eval and rewrite the tree as simply the
value given for the field (1 in the example above).

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

gcc/ada/

	* exp_ch6.adb: Fix typo in comment.
	* sem_ch3.adb (Access_Subprogram_Declaration): Add missing call
	to Create_Extra_Formals. Remove obsolete bootstrap check.
	* sem_eval.adb (Eval_Selected_Component): Simplify a
	selected_component on an aggregate.