The xen-bridge service accepts the option prefixLength, but does not
use it to set the actual netmask on the bridge. This commit makes
it set the correct netmask.

Needed to build an executable that uses OpenMP with clang. This
includes a header file and a library that clang will link into an
executable whose source makes use of ‘omp‘ pragmas.

This allows cross-compiling it.

The dependencies were added for purescript 0.10.7 and are no longer needed since
the override is gone.

Add the option virtualisation.xen.domain.extraConfig, which
allows overriding options passed to xendomains.

Provide the option forwardDns in virtualisation.xen.bridge, which
enables forwarding of DNS queries to the default resolver, allowing
outside internet access for the xen guests.

stable: 57.0.2987.133 -> 58.0.3029.96
beta: 58.0.3029.68 -> 59.0.3071.36
dev: 59.0.3067.0 -> 60.0.3088.3

Contains a fix for CVE-2017-8301: TLS verification vulnerability in
LibreSSL 2.5.1 - 2.5.3 [1][2]

[1]: http://seclists.org/oss-sec/2017/q2/145
[2]: libressl/portable#307

IPFS uses the environment variable IPFS_PATH to determine where to look for it's data, which wasn't set previously therefore ignoring the dataDir attribute

The Sierra linker added a limit on the number of paths that any one
dynamic library (`*.dylib`) can reference.  This causes problems when
a Haskell library has many immediate dependencies (#22810).

We follow a similar fix as GHC/Cabal/Stack: for each derivation,
create a new directory with symlinks to all the dylibs of its immediate
dependencies, and patch its package DB to reference that directory
using the new `dynamic-library-dirs` field.

Note that this change is a no-op for older versions of GHC, i.e., they will
continue to fail on some packages as before.

Also note that this change causes the bootstrapped versions of GHC to be
recompiled, since they depend on `hscolour` which is built by
`generic-builder.nix`.

Tested by building the `stack` binary as described in #22810.

libressl: 2.5.3 -> 2.5.4

See https://lists.gnu.org/archive/html/info-gnu/2017-05/msg00003.html
for release information