paxctl: Use http instead of https

This is needed since paxctl is going to be added to stdenv but
early stdenv curl does not support https.
grsecurity: Add paxctl, paxmark and stdenv.needsPax to stdenv
spl: Fix compilation with grsecurity's constify plugin and kernels < 3.8
qimageblitz: Mark stack as non-executable (patch taken from Gentoo)

This allows applications such as okular and kolourpaint to run in
grsecurity kernels, which disallow executable stacks by default.
firefox: Add support for grsecurity
chromium: Add support for grsecurity
polkit: Add support for grsecurity
llvm: Add support for grsecurity
gcc: Add support for grsecurity
oraclejdk7: Add support for grsecurity
spidermonkey: Add support for grsecurity
gstreamer: Add support for grsecurity
grub: Add support for grsecurity
mesa-noglu: Add support for grsecurity
ghc: Add support for grsecurity

In this case, we also need to specify compilation flags to mark stacks as
non-executable, otherwise PaX will not allow ghc or binaries built by ghc
to run.  This is what gentoo-hardened does as well.
openjdkBootstrap: Add support for grsecurity