Fix codes for compiling with mbedTLS

Clean up codes. (+6 squashed commit)

Squashed commit:

[4126d9e] Update build scripts

[2ee5027] Update CMake module

[71da951] Update build scripts

[dea8d3f] Update CMake script

[92113ba] Clean up codes and update build script

src/speedtestutil.cpp

@@ -5,7 +5,6 @@
 #include <time.h>
 
 #include <rapidjson/document.h>
-#include <pcrecpp.h>
 
 #include "misc.h"
 #include "printout.h"