flambda-backend: Implement -no-approx and -no-code in flambda-backend ocamlobjinfo (#2737)

* Implement `-no-approx` and `-no-code` in flambda-backend `ocamlobjinfo`

The old `-no-approx` and `-no-code` options are currently parsed but ignored.
This is inconvenient, since the output for an flambda2 .cmx can be screenfuls
long even for relatively small modules.

This PR implements `-no-approx` by just suppressing .cmx export information
altogether (roughly equivalent to what the old one did).

Also implements `-no-code` by doing exactly the same thing as
`-no-approx`. (Which does indeed mean there's no code.)

* Also suppress zero-alloc info

It's not as noisy as the full export info but it does make tests more sensitive.

* Add conditional printing to Flambda_cmx_format

* Better condition

* Add a test case with `-no-code` but not `-no-approx`

This exercises the separate `-no-approx` implementation from
lukemaurer#2.

---------

Co-authored-by: Vincent Laviron <[email protected]>

Author: lukemaurer

testsuite/tests/tool-ocamlobjinfo/question.ml

@@ -8,11 +8,18 @@
  check-ocamlopt.byte-output;
  {
    ocamlobjinfo;
+
+   program = "-no-code -no-approx question.cmx";
+   ocamlobjinfo;
+
+   program = "-no-code question.cmx";
+   ocamlobjinfo;
+
    check-program-output;
  }{
    program = "question.cmx";
    ocamlobjinfo;
-   (* The cmx output varies too much to check. We're just happy it didn't
+   (* The full cmx output varies too much to check. We're just happy it didn't
       segfault on us. *)
  }
 *)

testsuite/tests/tool-ocamlobjinfo/question.reference

@@ -8,3 +8,64 @@ Interfaces imported:
 	00000000000000000000000000000000	Question
 	00000000000000000000000000000000	CamlinternalFormatBasics
 Implementations imported:
+File question.cmx
+Name: Question
+CRC of implementation: 00000000000000000000000000000000
+Globals defined:
+	Question
+Interfaces imported:
+	00000000000000000000000000000000	Stdlib
+	00000000000000000000000000000000	Question
+	00000000000000000000000000000000	CamlinternalFormatBasics
+Implementations imported:
+Flambda 2 unit with export information
+Currying functions:
+Apply functions:
+Send functions:
+Force link: no
+File question.cmx
+Name: Question
+CRC of implementation: 00000000000000000000000000000000
+Globals defined:
+	Question
+Interfaces imported:
+	00000000000000000000000000000000	Stdlib
+	00000000000000000000000000000000	Question
+	00000000000000000000000000000000	CamlinternalFormatBasics
+Implementations imported:
+Flambda 2 export information:
+Original unit: Question
+Typing env:
+((defined_symbols_without_equations ())
+ (code_age_relation
+  {(camlQuestion__answer_0_1_code camlQuestion__answer_0_0_code)})
+ (type_equations
+  {(Question.camlQuestion
+    (Val
+     (Variant
+      (blocks
+       ((alloc_mode Heap) (known
+         {(tag_0 => (Known 1), ((Val (= Question.camlQuestion__answer_1))))})
+        (other Bottom))) (tagged_imms (Naked_immediate ⊥)))))
+   (Question.camlQuestion__answer_1
+    (Val
+     ((alloc_mode Heap) (known
+       {((answer/0 ∷ 𝕍)
+         => (Known ((closures { (answer/0 ∷ 𝕍) }) (value_slots { }))),
+         ((function_types
+           {((answer/0 ∷ 𝕍)
+             (Ok (function_type (code_id camlQuestion__answer_0_1_code)
+                  (rec_info (Rec_info 0)))))})
+          (closure_types
+           ((function_slot_components_by_index
+             {((answer/0 ∷ 𝕍) (Val (= Question.camlQuestion__answer_1)))})))
+          (value_slot_types ((value_slot_components_by_index {})))))})
+      (other Bottom))))})
+ (aliases
+  ((canonical_elements {}) (aliases_of_canonical_names {})
+   (aliases_of_consts {}))))
+
+Currying functions:
+Apply functions:
+Send functions:
+Force link: no