[commit: ghc] ghc-8.4: Bump unix submodule back to 2.7 (a1e15c8)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : ghc-8.4
Link       : http://ghc.haskell.org/trac/ghc/changeset/a1e15c8f59092ef2d11be7966bd20688d8dc01e6/ghc

>---------------------------------------------------------------

commit a1e15c8f59092ef2d11be7966bd20688d8dc01e6
Author: Ben Gamari <ben at smart-cactus.org>
Date:   Fri Feb 23 16:57:33 2018 -0500

    Bump unix submodule back to 2.7


>---------------------------------------------------------------

a1e15c8f59092ef2d11be7966bd20688d8dc01e6
 libraries/unix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libraries/unix b/libraries/unix
index 41c5776..3172ec8 160000
--- a/libraries/unix
+++ b/libraries/unix
@@ -1 +1 @@
-Subproject commit 41c5776162b60e0739a7559ceab03b9c3a444516
+Subproject commit 3172ec893026869d1a458cf067790fce3b1e3eef