Revert unixsupport_unix.c to the upstream version when using runtime5

ocaml/otherlibs/unix/unixsupport_unix.c

@@ -20,9 +20,9 @@
 #include <caml/callback.h>
 #include <caml/memory.h>
 #include <caml/fail.h>
-/* BACKPORT
+#ifdef CAML_RUNTIME_5
 #include <caml/platform.h>
-*/
+#endif
 #include "unixsupport.h"
 #include "cst2constr.h"
 #include <errno.h>
@@ -291,6 +291,37 @@ int caml_unix_code_of_unix_error (value error)
 
 static const value * _Atomic caml_unix_error_exn = NULL;
 
+#ifdef CAML_RUNTIME_5
+
+void caml_unix_error(int errcode, const char *cmdname, value cmdarg)
+{
+  CAMLparam0();
+  CAMLlocal3(name, err, arg);
+  value res;
+  const value * exn;
+
+  exn = atomic_load_acquire(&caml_unix_error_exn);
+  if (exn == NULL) {
+    exn = caml_named_value("Unix.Unix_error");
+    if (exn == NULL)
+      caml_invalid_argument("Exception Unix.Unix_error not initialized,"
+                            " please link unix.cma");
+    atomic_store(&caml_unix_error_exn, exn);
+  }
+  arg = cmdarg == Nothing ? caml_copy_string("") : cmdarg;
+  name = caml_copy_string(cmdname);
+  err = caml_unix_error_of_code (errcode);
+  res = caml_alloc_small(4, 0);
+  Field(res, 0) = *exn;
+  Field(res, 1) = err;
+  Field(res, 2) = name;
+  Field(res, 3) = arg;
+  caml_raise(res);
+  CAMLnoreturn;
+}
+
+#else
+
 void caml_unix_error(int errcode, const char *cmdname, value cmdarg)
 {
   CAMLparam0();
@@ -326,6 +357,8 @@ void caml_unix_error(int errcode, const char *cmdname, value cmdarg)
   CAMLnoreturn;
 }
 
+#endif
+
 void caml_uerror(const char *cmdname, value cmdarg)
 {
   caml_unix_error(errno, cmdname, cmdarg);

ocaml/runtime/caml/config.h

@@ -16,6 +16,7 @@
 #ifndef CAML_CONFIG_H
 #define CAML_CONFIG_H
 
+/* CR ocaml 5 all-runtime5: remove this and all uses of it */
 #define CAML_RUNTIME_5
 
 /* CAML_NAME_SPACE was introduced in OCaml 3.08 to declare compatibility with