Fix LUA_R_INCL not being used on linux

SConscript

@@ -268,15 +268,16 @@ def findLibs(env, conf):
 			if not conf.CheckLib(['lua5.1', 'lua-5.1', 'lua51', 'lua']):
 				if platform != "Darwin" or not conf.CheckFramework("Lua"):
 					FatalError("lua5.1 development library not found or not installed")
-
+		foundpkg = False
 		if platform == "Linux":
 			try:
 				env.ParseConfig("pkg-config --cflags {0}".format(luaver))
 				env.ParseConfig("pkg-config --libs {0}".format(luaver))
 				env.Append(CPPDEFINES=["LUA_R_INCL"])
+				foundpkg = True
 			except:
 				pass
-		else:
+		if not foundpkg:
 			#Look for lua.h
 			foundheader = False
 			if GetOption('luajit'):