enable full GCC Stack-smashing protection for all OSes

- change our hardening options to use -fstack-protector-all even for
  Windows builds, as we recently switched to a newer compiler suite
- also removes an obsolete workaround for GCC 4.5
  (https://bugs.launchpad.net/ubuntu/+source/gcc-4.5/+bug/691722), which
  required to first set -fno-stack-protector, before -fstack-protector-all
build: Add -static for mingw builds

This avoids a dependency on libssp-0.dll when built with
-fstack-protector-all.
Merge pull request #1674

6ac0b3b build: Add -static for mingw builds (Wladimir J. van der Laan)
4e57e23 enable full GCC Stack-smashing protection for all OSes (Philip Kaufmann)