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- Move native txt2iff.c and xpm2iff.c to outdated/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

sys/amiga/winkey.c

@@ -12,12 +12,14 @@
 #include "winproto.h"
 #endif
 
-amii_nh_poskey(x, y, mod) int *x, *y, *mod;
+int
+amii_nh_poskey(coordxy *x, coordxy *y, int *mod)
 {
     struct amii_WinDesc *cw;
     WETYPE type;
     struct RastPort *rp;
     struct Window *w;
+    /* No entry log for nh_poskey -- too noisy (called constantly) */
 
     if (cw = amii_wins[WIN_MESSAGE]) {
         cw->wflags &= ~FLMAP_SKIP;
@@ -59,10 +61,11 @@ amii_nh_poskey(x, y, mod) int *x, *y, *mod;
 }
 
 int
-amii_nhgetch()
+amii_nhgetch(void)
 {
     int ch;
     struct amii_WinDesc *cw = amii_wins[WIN_MESSAGE];
+    /* No entry log for nhgetch -- too noisy (called constantly) */
 
     if (WIN_MAP != WIN_ERR && amii_wins[WIN_MAP]) {
         cursor_on(WIN_MAP);
@@ -75,15 +78,15 @@ amii_nhgetch()
 }
 
 void
-amii_get_nh_event()
+amii_get_nh_event(void)
 {
     /* nothing now - later I have no idea.  Is this just a Mac hook? */
 }
 
 void
-amii_getret()
+amii_getret(void)
 {
-    register int c;
+    int c;
 
     raw_print("");
     raw_print("Press Return...");