lua: allow overriding of LUA_CFLAGS

lua/CMakeLists.txt

@@ -4,13 +4,15 @@ PROJECT(uci C)
 
 SET(CMAKE_INSTALL_PREFIX /)
 
-FIND_PROGRAM(PKG_CONFIG pkg-config)
-IF(PKG_CONFIG)
-	EXECUTE_PROCESS(
-		COMMAND pkg-config --silence-errors --cflags lua5.1
-		OUTPUT_VARIABLE LUA_CFLAGS
-		OUTPUT_STRIP_TRAILING_WHITESPACE
-	)
+IF(NOT LUA_CFLAGS)
+	FIND_PROGRAM(PKG_CONFIG pkg-config)
+	IF(PKG_CONFIG)
+		EXECUTE_PROCESS(
+			COMMAND pkg-config --silence-errors --cflags lua5.1
+			OUTPUT_VARIABLE LUA_CFLAGS
+			OUTPUT_STRIP_TRAILING_WHITESPACE
+		)
+	ENDIF()
 ENDIF()
 
 ADD_DEFINITIONS(-Os -Wall -Werror --std=gnu99 -g3 -I.. ${LUA_CFLAGS})