Improve hardening flags

This closes #317 (closed)

It has taken sometime to both deduce what we actually needed to do, as it turns out we enable PIE by default when building GCC, in gcc-stage2.bst and gcc.bst. So the spec files were no longer needed.

This currently splits the gcc/ld flags into default variables, which can then be extended upon based on the 'target-arch' in the Environment.

All flags have been provided by:

• https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/master/f/buildflags.md
• https://developers.redhat.com/blog/2018/03/21/compiler-and-linker-flags-gcc/