patch 8.2.0320: no Haiku support

Problem:    No Haiku support.
Solution:   Add support for Haiku. (Emir Sari, closes #5605)

src/gui_haiku.h

@@ -0,0 +1,51 @@
+/* vi:set ts=8 sts=4 sw=4:
+ *
+ * VIM - Vi IMproved		by Bram Moolenaar
+ *				GUI support by Olaf "Rhialto" Seibert
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ *
+ * Haiku GUI.
+ *
+ * Based on "GUI support for the Buzzword Enhanced Operating System for PPC."
+ *
+ */
+
+/*
+ * This file must be acceptable both as C and C++.
+ * The BeOS API is defined in terms of C++, but some classes
+ * should be somewhat known in the common C code.
+ */
+
+// System classes
+
+struct BMenu;
+struct BMenuItem;
+struct BPictureButton;
+
+// Our own Vim-related classes
+
+struct VimApp;
+struct VimFormView;
+struct VimTextAreaView;
+struct VimWindow;
+struct VimScrollBar;
+
+// Locking functions
+
+extern int vim_lock_screen();
+extern void vim_unlock_screen();
+
+#ifndef __cplusplus
+
+typedef struct BMenu BMenu;
+typedef struct BMenuItem BMenuItem;
+typedef struct BPictureButton BPictureButton;
+typedef struct VimWindow VimWindow;
+typedef struct VimFormView VimFormView;
+typedef struct VimTextAreaView VimTextAreaView;
+typedef struct VimApp VimApp;
+typedef struct VimScrollBar VimScrollBar;
+
+#endif