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- Move native txt2iff.c and xpm2iff.c to outdated/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

include/amiconf.h

@@ -48,13 +48,9 @@ typedef long off_t;
 #define PATHLEN 130
 
 /* data librarian defs */
-#ifndef NOCWD_ASSUMPTIONS
-#define DLBFILE "NetHack:nhdat"   /* main library */
-#define DLBFILE2 "NetHack:nhsdat" /* sound library */
-#else
 #define DLBFILE "nhdat"   /* main library */
-#define DLBFILE2 "nhsdat" /* sound library */
-#endif
+/* nhsdat sound library not used in 3.7 */
+#undef DLBFILE2
 
 #ifndef CROSS_TO_AMIGA
 #define FILENAME_CMP stricmp /* case insensitive */