[Ada] Fix handling of array renamings

[Ada] Fix handling of array renamings

Compilers can materialize renamings of arrays (or of accesses to arrays)
in Ada into variables whose types are references to the actual array
types.  Before this change, trying to use such an array renaming yielded
an error in GDB:

    (gdb) print my_array(1)
    cannot subscript or call a record
    (gdb) print my_array_ptr(1)
    cannot subscript or call something of type `(null)'

This behavior comes from bad handling for array renamings, in particular
the OP_FUNCALL expression operator handling from ada-lang.c
(ada_evaluate_subexp): in one place we turn the reference into a
pointer, but the code that follows expect the value to be an array.

This patch fixes how we handle references in call/subscript evaluation
so that we turn these references into the actual array values instead of
pointers to them.

gdb/ChangeLog:

	* ada-lang.c (ada_evaluate_subexp) <OP_FUNCALL>: When the input
	value is a reference, actually dereference it in order to get
	the underlying value.

gdb/testsuite/ChangeLog:

	* gdb.ada/array_ptr_renaming.exp: New testcase.
	* gdb.ada/array_ptr_renaming/foo.adb: New file.
	* gdb.ada/array_ptr_renaming/pack.ads: New file.

Tested on x86_64-linux, no regression.