Merge pull request #445 from peti/switch-stdenv-to-gcc-4.8.0

Switch stdenv to GCC 4.8.0.
gcc48: turn on PGO on x86*, see #445
gcc42: fix build via a patch from arch
ruby19: fix build via a patch-level update
Merge changes from branch 'master' into stdenv-updates.

Conflicts:
	pkgs/development/libraries/icu/default.nix
	pkgs/tools/misc/coreutils/default.nix
release-small-linux.nix: a variant of release-small.nix that builds only on x86_64-linux