patch 8.1.2224: cannot build Amiga version

Problem:    Cannot build Amiga version.
Solution:   Add dummy mch_setmouse(). (Ola Söder, closes #5126)
diff --git a/src/os_amiga.c b/src/os_amiga.c
index aff24c5..8627cb6 100644
--- a/src/os_amiga.c
+++ b/src/os_amiga.c
@@ -658,6 +658,12 @@
 }
 #endif
 
+    void
+mch_setmouse(int on UNUSED)
+{
+    // TODO: implement
+}
+
 /*
  * Insert user name in s[len].
  */
diff --git a/src/proto/os_amiga.pro b/src/proto/os_amiga.pro
index b781680..7aaf171 100644
--- a/src/proto/os_amiga.pro
+++ b/src/proto/os_amiga.pro
@@ -15,6 +15,7 @@
 void mch_restore_title(int which);
 int mch_can_restore_title(void);
 int mch_can_restore_icon(void);
+void mch_setmouse(int on);
 int mch_get_user_name(char_u *s, int len);
 void mch_get_host_name(char_u *s, int len);
 long mch_get_pid(void);
diff --git a/src/version.c b/src/version.c
index b0fdab2..62a4888 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2224,
+/**/
     2223,
 /**/
     2222,