Revive Amiga port for NetHack 3.7

Update the Amiga Intuition window port (AMII/AMIV) for the 3.7
window_procs API. Key changes:

- Update all window function signatures for 3.7
- Add assembly trampolines for AmigaOS register-based callbacks
- Convert all K&R function definitions to C99
- Add cross-compilation build system (cross-pre1/pre2/post.370)
  using bebbo's m68k-amigaos-gcc with -noixemul -std=gnu17 -m68000
- Clipping fixes: viewport centering, simplified ScrollRaster,
  duplicate Ctrl-R suppression, glyph buffer invalidation
- Add menucolor support in menu rendering
- Move native txt2iff.c and xpm2iff.c to outdated/
- Add nethack.cnf and README.amiga

src/rip.c

@@ -9,7 +9,8 @@
    necessarily have to be used by a binary with multiple window-ports */
 
 #if defined(TTY_GRAPHICS) || defined(X11_GRAPHICS) || defined(GEM_GRAPHICS) \
-    || defined(DUMPLOG) || defined(CURSES_GRAPHICS) || defined(SHIM_GRAPHICS)
+    || defined(DUMPLOG) || defined(CURSES_GRAPHICS) || defined(SHIM_GRAPHICS) \
+    || defined(AMII_GRAPHICS)
 #define TEXT_TOMBSTONE
 #endif
 #if defined(mac) || defined(__BEOS__)