last known Amiga cross-compile -> outdated

Place the last known Amiga cross-compile effort into the outdated folder
tree.

This shell script was meant to be run from the top of the NetHack tree:
    outdated/sys/unix/cross-amiga.sh
It attempts two things:
1. obtain the source-code for the Amiga cross compiler and build it
   from scratch. Warning: it pulls a number of the required packages
   from the internet and installs them. (Linux was tested, but the macOS
   usage never was).
2. move the outdated hints file and hints include files for Amiga
   into the live tree for someone attempting to resurrect an Amiga port.
   It doesn't tinker with any of the files needed for the NetHack-3.7
   work-in-progess for other platforms.

Once the shell script completes those things, the cross-compile build
steps would be:
  i) cd sys/unix ; sh setup.sh hints/cross-amiga ; cd ../..
 ii) make CROSS_TO_AMIGA=1 all
iii) make CROSS_TO_AMIGA=1 package

outdated/sys/amiga/amidos.c

@@ -42,6 +42,7 @@
 extern char Initialized;
 extern struct window_procs amii_procs;
 struct ami_sysflags sysflags = {0};
+FILE *fopenp(const char *, const char *);
 
 #ifndef __SASC_60
 int Enable_Abort = 0; /* for stdio package */