Silence some macOS build warnings

* src/image.c (native_image_type): Declare static.
* src/keyboard.c (lispy_function_keys): Declare static on NS.
* src/nsmenu.m (context_menu_value):
* src/nsterm.m (ns_frame_parm_handlers): Move extern declarations...
* src/nsterm.h: ...here.
* test/src/emacs-module-resources/mod-test.c: Add extern declaration.

src/image.c

@@ -12744,7 +12744,7 @@ static struct image_type const image_types[] =
 };
 
 #if HAVE_NATIVE_IMAGE_API
-struct image_type native_image_type =
+static struct image_type native_image_type =
   { SYMBOL_INDEX (Qnative_image), native_image_p, native_image_load,
     image_clear_image };
 #endif

src/keyboard.c

@@ -5396,6 +5396,10 @@ static const char *const lispy_kana_keys[] =
 
 /* You'll notice that this table is arranged to be conveniently
    indexed by X Windows keysym values.  */
+#ifdef HAVE_NS
+/* FIXME: Why are we using X11 keysym values for NS?  */
+static
+#endif
 const char *const lispy_function_keys[] =
   {
     /* X Keysym value */

src/nsmenu.m

@@ -47,7 +47,6 @@
 #endif
 
 
-extern long context_menu_value;
 EmacsMenu *svcsMenu;
 /* Nonzero means a menu is currently active.  */
 static int popup_activated_flag;

src/nsterm.h

@@ -921,6 +921,8 @@ struct ns_display_info
 /* This is a chain of structures for all the NS displays currently in use.  */
 extern struct ns_display_info *x_display_list;
 
+extern long context_menu_value;
+
 struct ns_output
 {
 #ifdef __OBJC__
@@ -1269,6 +1271,8 @@ extern void ns_finish_events (void);
 
 extern double ns_frame_scale_factor (struct frame *);
 
+extern frame_parm_handler ns_frame_parm_handlers[];
+
 #ifdef NS_IMPL_GNUSTEP
 extern char gnustep_base_version[];  /* version tracking */
 #endif

src/nsterm.m

@@ -5438,7 +5438,6 @@ static Lisp_Object ns_string_to_lispmod (const char *s)
    redisplay interface.  In addition, many of the ns_ methods have
    code that is shared with all terms, indicating need for further
    refactoring.  */
-extern frame_parm_handler ns_frame_parm_handlers[];
 static struct redisplay_interface ns_redisplay_interface =
 {
   ns_frame_parm_handlers,

test/src/emacs-module-resources/mod-test.c

@@ -46,6 +46,7 @@ uintptr_t _beginthread (void (__cdecl *) (void *), unsigned, void *);
 #include <gmp.h>
 #include <emacs-module.h>
 
+extern int plugin_is_GPL_compatible;
 int plugin_is_GPL_compatible;
 
 #if INTPTR_MAX <= 0