Do not try to auto-guess Lua directories from the path to the interpreter,
it does not work with the wrapper set up by lua-single.eclass. Use the
values of LUA, LUA_BINDIR and LUA_SHAREDIR provided by the ebuild instead.
--- a/Makefile
+++ b/Makefile
@@ -1,14 +1,9 @@
-LUA= $(shell echo `which lua`)
-LUA_BINDIR= $(shell echo `dirname $(LUA)`)
-LUA_PREFIX= $(shell echo `dirname $(LUA_BINDIR)`)
-LUA_SHAREDIR=$(LUA_PREFIX)/share/lua/5.1
-
 _REPODIR != cd "$(shell dirname $(firstword $(MAKEFILE_LIST)))/" && pwd
 
 ldoc:
 
 install: install_parts
-	@echo "lua $(LUA_SHAREDIR)/ldoc.lua \$$*" > "$(DESTDIR)$(LUA_BINDIR)/ldoc"
+	@echo "$(LUA) $(LUA_SHAREDIR)/ldoc.lua \$$*" > "$(DESTDIR)$(LUA_BINDIR)/ldoc"
 	@chmod -v +x "$(DESTDIR)$(LUA_BINDIR)/ldoc"
 
 install_luajit: install_parts