Fix bug in Ada aggregate assignment

Fix bug in Ada aggregate assignment

The expression rewrite caused a regression in the internal AdaCore
test suite.  The bug was that I had dropped a bit of code from
aggregate assignment -- assign_aggregate used to return the container,
which I thought was redundant, but which can actually change during
the call.  There was no test for this case in the tree, so I've added
one.

gdb/ChangeLog
2021-03-15  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_aggregate_operation::assign_aggregate): Return
	container.
	(ada_assign_operation::evaluate): Update.
	* ada-exp.h (class ada_aggregate_operation) <assign_aggregate>:
	Change return type.

gdb/testsuite/ChangeLog
2021-03-15  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/assign_arr/target_wrapper.ads (IArray, Put, Do_Nothing):
	Declare.
	* gdb.ada/assign_arr/target_wrapper.adb: New file.
	* gdb.ada/assign_arr/main_p324_051.adb (IValue): New variable.
	Call Put.
	* gdb.ada/assign_arr.exp: Update.