support for build with current Lua version 5.4.3

On some platforms this may require:
	make spotless
	make fetch-lua

I did attempt to force a reminder message about the latter to
Makefile.top this time, and hope that works correctly for everyone.

sys/msdos/fetch-cross-compiler.sh

@@ -12,7 +12,7 @@ if [ -z "$GCCVER" ]; then
 fi
 
 if [ -z "$LUA_VERSION" ]; then
-	export LUA_VERSION=5.4.2
+	export LUA_VERSION=5.4.3
 fi
 
 if [ ! -d "$(pwd)/lib" ]; then