This moves all URL references to Trac Wiki to their corresponding
GitLab counterparts.

This substitution is classified as follows:

1. Automated substitution using sed with Ben's mapping rule [1]
    Old: ghc.haskell.org/trac/ghc/wiki/XxxYyy...
    New: gitlab.haskell.org/ghc/ghc/wikis/xxx-yyy...

2. Manual substitution for URLs containing `#` index
    Old: ghc.haskell.org/trac/ghc/wiki/XxxYyy...#Zzz
    New: gitlab.haskell.org/ghc/ghc/wikis/xxx-yyy...#zzz

3. Manual substitution for strings starting with `Commentary`
    Old: Commentary/XxxYyy...
    New: commentary/xxx-yyy...

See also !539

[1]: https://gitlab.haskell.org/bgamari/gitlab-migration/blob/master/wiki-mapping.json

Summary:
building libffi docs with our intree-libffi seems
rather pointless.

Reviewers: bgamari, austin

Reviewed By: bgamari

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D4054

This is rather annoying. I'd prefer to have a stable release to
use. However libffi-3.2.1 has been released November 12, 2014, and
libffi-4 is TBD. See also https://github.com/libffi/libffi/issues/296

The core reason for this change is that llvm changed the supported
assembly to unified syntax, which libffi-3.2.1 does not use, and hence
fails to compile for arm with llvm. For refence, see the following
issue: https://github.com/libffi/libffi/issues/191.

This diff contains a script to generate a tarball for the
`libffi-tarballs` repository from the libffi GitHub repository; as well
as the necessary changes to the build system.

Updates libffi-tarballs submodule.

Reviewers: austin, bgamari, hvr

Subscribers: hvr, erikd, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3574

This reverts commit 8d4bce42de7929b0dec7e7d68e66bcfc4d266322.

This is rather annoying. I'd prefer to have a stable release to
use. However libffi-3.2.1 has been released November 12, 2014, and
libffi-4 is TBD. See also https://github.com/libffi/libffi/issues/296

The core reason for this change is that llvm changed the supported
assembly to unified syntax, which libffi-3.2.1 does not use, and hence
fails to compile for arm with llvm. For refence, see the following
issue: https://github.com/libffi/libffi/issues/191

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, snowleopard

Differential Revision: https://phabricator.haskell.org/D3349

Reviewers: bgamari, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1589

GHC Trac Issues: #10238

Using `:` as sed-`s`-expr separator is not a good idea on windows, as
this can result in an expression like

   's:@INSTALL@:$(subst ../install-sh,E:/msys64/home/foo/ghc/install-sh,@INSTALL@):g'

(note the `E:/` drive component)

Using `|` instead of `:` has less risk of collision with the substitution expression

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1494

GHC Trac Issues: #11109

We only support building GHC on mys2 nowadays, see
https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows.

This (partially) reverts various commits from a few years ago, among which:
  * 5775d5142da227d65fb86994d363eb16841ee642
    "Add OSTYPE build-system variable, and use it"
  * 3fb8c431824aa2f3bd979e35d1a283546fcfbe74
    "Fix building libgmp on cygwin"
  * cdbb4720c424500adb57cbbef69721d0b039fa46
    "Fix cmd invocation by libffi cuild system on Windows 7 cygwin"
  * e8121501ee3549a35e954726ccfd871ac9d51f83
    "Fix dblatex and xml* tool detection on Windows"

Reviewed by: austin, Phyx

Differential Revision: https://phabricator.haskell.org/D1155