Add some support for Alpine Linux system Lua package

Requires apk add lua5.4-dev (for the C Lua headers)

sys/unix/Makefile.top

@@ -121,13 +121,14 @@ DAT = $(DATNODLB) $(DATDLB)
 RECOVERBIN = recover
 
 # Lua
-LUAHEADERS = lib/lua-$(LUA_VERSION)/src
-LUATESTTARGET = $(LUAHEADERS)/lua.h
-LUATOP = $(LUAHEADERS)
-LUAMAKEFLAGS = CC='$(CC)' SYSCFLAGS='$(SYSCFLAGS)'
-LUA2NHTOP = ../../..
-LUABASELIB = liblua-$(LUA_VERSION).a
-TOPLUALIB = lib/lua/$(LUABASELIB)
+LUAHEADERS ?= lib/lua-$(LUA_VERSION)/src
+LUATESTTARGET ?= $(LUAHEADERS)/lua.h
+LUATOP ?= $(LUAHEADERS)
+LUAMAKEFLAGS ?= CC='$(CC)' SYSCFLAGS='$(SYSCFLAGS)'
+LUA2NHTOP ?= ../../..
+LUABASELIB ?= liblua-$(LUA_VERSION).a
+TOPLUALIB ?= lib/lua/$(LUABASELIB)
+LUAHPREFIX ?= ../
 
 ALLDEP = $(PRECHECK) $(GAME) recover Guidebook $(VARDAT) spec_levs check-dlb
 
@@ -149,12 +150,12 @@ $(TOPLUALIB): $(LUATOP)/liblua.a
 
 include/nhlua.h: $(TOPLUALIB)
 	echo '/* nhlua.h - generated by top Makefile */' > $@
-	@echo '#include "../$(LUAHEADERS)/lua.h"' >> $@
+	@echo '#include "$(LUAHPREFIX)$(LUAHEADERS)/lua.h"' >> $@
 	@sed -e '/(lua_error)/!d' \
 		-e '/(lua_error)/s/LUA_API/ATTRNORETURN LUA_API/1' \
 		-e '/(lua_error)/s/;/ NORETURN;/1' < $(LUAHEADERS)/lua.h >> $@
-	@echo '#include "../$(LUAHEADERS)/lualib.h"' >> $@
-	@echo '#include "../$(LUAHEADERS)/lauxlib.h"' >> $@
+	@echo '#include "$(LUAHPREFIX)$(LUAHEADERS)/lualib.h"' >> $@
+	@echo '#include "$(LUAHPREFIX)$(LUAHEADERS)/lauxlib.h"' >> $@
 	@echo '/*nhlua.h*/' >> $@
 # LUATESTTARGET is this by default
 lib/lua-$(LUA_VERSION)/src/lua.h: