Add hardening flags to the Makefile

[jvoisin]

Currently, the Makefile doesn't contain any hardening flags :/

[buixor]

Makefile itself is only used for unit tests, fuzzing, code coverage etc. It's the config file in the naxsi_src/ directory that is used by nginx for compilation. So for me that's out of our scope, and it would be fairely intrusive to try to push our compilation options ?

Thoughts ?

[jvoisin]

I hope that adding stuff into the config file won't put them for the whole compilation process: this would be ridiculous. We should indeed add options in this file.