patch 9.1.0018: use of #if instead of #ifdef

Problem:  use of #if instead of #ifdef
Solution: use correct form of #ifdef

`#if FEAT_GUI_HAIKU` was used mistakenly. Use the correct form
`#ifdef FEAT_GUI_HAIKU` instead.

closes: #13843

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/gui.h

@@ -176,7 +176,7 @@ typedef struct GuiScrollbar
 				// to reduce the count.
 #endif
 
-#if FEAT_GUI_HAIKU
+#ifdef FEAT_GUI_HAIKU
     VimScrollBar *id;		// Pointer to real scroll bar
 #endif
 #ifdef FEAT_GUI_PHOTON

src/structs.h

@@ -4333,7 +4333,7 @@ struct VimMenu
     HMENU	submenu_id;	    // If this is submenu, add children here
     HWND	tearoff_handle;	    // hWnd of tearoff if created
 #endif
-#if FEAT_GUI_HAIKU
+#ifdef FEAT_GUI_HAIKU
     BMenuItem  *id;		    // Id of menu item
     BMenu  *submenu_id;		    // If this is submenu, add children here
 # ifdef FEAT_TOOLBAR

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    18,
 /**/
     17,
 /**/