flambda-backend: Fixes for runtest on runtime5 (#2058)

* Fixing tests/backend/checkmach/

* Fix ocaml/utils/symbol.ml{,i} to force runtime4-style symbols, for tests

* Disable flexpect when stack allocation is disabled

* Fix runtime dir path in tests/simd/dune

* Force runtime4-style symbols in flexpect

* Add missing dependency needed by the Makefile

* Fix simd stubs inclusion in the runtime .a files

* More checkmach test fixing

Makefile

@@ -720,6 +720,7 @@ runtime_COMMON_C_SOURCES = \
   runtime_events \
   shared_heap \
   signals \
+  simd \
   skiplist \
   startup_aux \
   str \

runtime/dune

@@ -42,6 +42,7 @@
    ../.depend
    ../.depend.menhir
    ../config.status
+   ../stdlib/StdlibModules
    (glob_files caml/*.h)
    (glob_files *.h)
    caml/domain_state.tbl

utils/symbol.ml

@@ -46,7 +46,13 @@ include Identifiable.Make (struct
 end)
 
 let caml_symbol_prefix = "caml"
-let separator = if Config.runtime5 then "." else "__"
+
+let force_runtime4_symbols = ref false
+
+let separator () =
+  if Config.runtime5 && not !force_runtime4_symbols then "." else "__"
+
+let force_runtime4_symbols () = force_runtime4_symbols := true
 
 let linkage_name t = t.linkage_name
 
@@ -74,7 +80,7 @@ let linkage_name_for_compilation_unit comp_unit =
       let pack_names =
         CU.Prefix.to_list for_pack_prefix |> List.map CU.Name.to_string
       in
-      String.concat separator (pack_names @ [name])
+      String.concat (separator ()) (pack_names @ [name])
   in
   caml_symbol_prefix ^ suffix
   |> Linkage_name.of_string
@@ -98,7 +104,7 @@ let for_name compilation_unit name =
     linkage_name_for_compilation_unit compilation_unit |> Linkage_name.to_string
   in
   let linkage_name =
-    prefix ^ separator ^ name |> Linkage_name.of_string
+    prefix ^ (separator ()) ^ name |> Linkage_name.of_string
   in
   { compilation_unit;
     linkage_name;

utils/symbol.mli

@@ -45,3 +45,7 @@ val linkage_name_for_ocamlobjinfo : t -> string
 include Identifiable.S with type t := t
 
 val is_predef_exn : t -> bool
+
+(* Temporary means by which to force symbol names to use __.  Only for use
+   for flambda2 flexpect tests. *)
+val force_runtime4_symbols : unit -> unit