plan9 port maintenance (#1756)

* plan9: fix regressions

* plan9: unopaque struct pointer

---------

Co-authored-by: Noam Preil <noam@pixelhero.dev>

Author: pixelherodev

src/core/io.c

@@ -424,7 +424,11 @@ static void io_file_marshal(void *p, JanetMarshalContext *ctx) {
         if (iof->flags & JANET_FILE_NOT_CLOSEABLE) {
             fno = fileno(iof->file);
         } else {
+#ifdef JANET_PLAN9
+			fno = dup(fileno(iof->file), -1);
+#else
             fno = dup(fileno(iof->file));
+#endif
         }
 #endif
         janet_marshal_int(ctx, fno);

src/core/marsh.c

@@ -30,13 +30,6 @@
 #include "util.h"
 #endif
 
-struct JanetMarshalContext {
-    void *m_state;
-    void *u_state;
-    int flags;
-    const uint8_t *data;
-    const JanetAbstractType *at;
-};
 
 typedef struct {
     JanetBuffer *buf;

src/core/os.c

@@ -287,7 +287,11 @@ JANET_CORE_FN(os_exit,
     }
     janet_deinit();
     if (argc >= 2 && janet_truthy(argv[1])) {
+#ifdef JANET_PLAN9
+		exits(nil);
+#else
         _Exit(status);
+#endif
     } else {
         exit(status);
     }

src/include/janet.h

@@ -1202,6 +1202,13 @@ struct JanetParser {
 };
 
 /* A context for marshaling and unmarshaling abstract types */
+struct JanetMarshalContext {
+    void *m_state;
+    void *u_state;
+    int flags;
+    const uint8_t *data;
+    const JanetAbstractType *at;
+};
 typedef struct JanetMarshalContext JanetMarshalContext;
 
 /* Defines an abstract type. Use a const pointer to one of these structures