Do hardening of builds

The following discussion from !17 (merged) should be addressed:

• @akwizgran started a discussion: (+2 comments)

  I think you mentioned somewhere that you had to drop -O3 (which is commented as "needed for FORTIFY_SOURCE" in the Linux build), but I couldn't find where you mentioned it. I can't remember where the FORTIFY_SOURCE comment came from - possibly the Guardian Project's original Makefile? Any idea whether it's important?