Add the REQUIRE_LUAJIT option (#5526)

lib/CMakeLists.txt

@@ -1,13 +1,20 @@
 # LuaJIT
 option(ENABLE_LUAJIT "Enable LuaJIT support" TRUE)
 set(USE_LUAJIT FALSE PARENT_SCOPE)
+option(REQUIRE_LUAJIT "Require LuaJIT support" FALSE)
+if(REQUIRE_LUAJIT)
+	set(ENABLE_LUAJIT TRUE)
+endif()
 if(ENABLE_LUAJIT)
 	find_package(LuaJIT)
 	if(LUAJIT_FOUND)
 		set(USE_LUAJIT TRUE)
 		set(USE_LUAJIT TRUE PARENT_SCOPE)
 		message (STATUS "Using LuaJIT provided by system.")
-	endif(LUAJIT_FOUND)
+	elseif(REQUIRE_LUAJIT)
+		message(FATAL_ERROR "LuaJIT not found whereas REQUIRE_LUAJIT=\"TRUE\" is used.\n"
+			"To continue, either install LuaJIT or do not use REQUIRE_LUAJIT=\"TRUE\".")
+	endif()
 else()
 	message (STATUS "LuaJIT detection disabled! (ENABLE_LUAJIT=0)")
 endif()