be more consistent with CROSS_TO_target macro names for cross-compiles

-DCROSS_TO_MSDOS	msdos cross-compile (djgpp cross-compiler)
-DCROSS_TO_AMIGA	Amiga cross-compile
-DCROSS_TO_WASM		wasm cross-compile (emscripten)

outdated/sys/amiga/winami.c

@@ -3,7 +3,7 @@
  */
 /* NetHack may be freely redistributed.  See license for details. */
 
-#ifndef AMIGA_CROSS
+#ifndef CROSS_TO_AMIGA
 #include "NH:sys/amiga/windefs.h"
 #include "NH:sys/amiga/winext.h"
 #include "NH:sys/amiga/winproto.h"
@@ -15,7 +15,7 @@
 
 #include "dlb.h"
 
-#ifdef AMIGA_CROSS
+#ifdef CROSS_TO_AMIGA
 #define strnicmp strncmpi
 #endif