gnu: haskell-mode: Fix test failure.

Fixes <https://bugs.gnu.org/31726>.

Thanks to Jack Hill <jackhill@jackhill.us> for exploring different solutions
at <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=31726>.

* gnu/packages/patches/haskell-mode-unused-variables.patch,
gnu/packages/patches/haskell-mode-make-check.patch: New files.
* gnu/local.mk (dist_patch_DATA): Add them.
* gnu/packages/emacs.scm (haskell-mode)[source]: Use them.
[arguments]: Adjust 'pre-build' phase to embed file name.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/patches/haskell-mode-unused-variables.patch

@@ -0,0 +1,44 @@
+Copied verbatim from upstream repository.
+
+From cee22450ee30e79952f594796721dc6b17798ee6 Mon Sep 17 00:00:00 2001
+From: Sascha Wilde <wilde@sha-bang.de>
+Date: Fri, 23 Sep 2016 15:35:59 +0200
+Subject: [PATCH] Removed unused lexical variables.
+
+---
+ haskell-lexeme.el  | 3 +--
+ haskell-process.el | 4 +---
+ 2 files changed, 2 insertions(+), 5 deletions(-)
+
+diff --git a/haskell-lexeme.el b/haskell-lexeme.el
+index 4256a79..b832560 100644
+--- a/haskell-lexeme.el
++++ b/haskell-lexeme.el
+@@ -138,8 +138,7 @@ When match is successful, match-data will contain:
+   (match-text 2) - whole qualified identifier
+   (match-text 3) - unqualified part of identifier
+   (match-text 4) - closing backtick"
+-  (let ((begin (point))
+-        (match-data-old (match-data))
++  (let ((match-data-old (match-data))
+         first-backtick-start
+         last-backtick-start
+         qid-start
+diff --git a/haskell-process.el b/haskell-process.el
+index b4efba2..4f3f859 100644
+--- a/haskell-process.el
++++ b/haskell-process.el
+@@ -160,9 +160,7 @@ HPTYPE is the result of calling `'haskell-process-type`' function."
+ (defun haskell-process-log (msg)
+   "Effective append MSG to the process log (if enabled)."
+   (when haskell-process-log
+-    (let* ((append-to (get-buffer-create "*haskell-process-log*"))
+-           (windows (get-buffer-window-list append-to t t))
+-           move-point-in-windows)
++    (let* ((append-to (get-buffer-create "*haskell-process-log*")))
+       (with-current-buffer append-to
+         ;; point should follow insertion so that it stays at the end
+         ;; of the buffer
+-- 
+2.18.0
+