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-make-check.patch

@@ -0,0 +1,35 @@
+Copied from upstream repository.
+Hunk #2 is removed since it cannot be applied and it is not needed.
+
+From 7cead7137bf54851c1b7df5a3854351296d21276 Mon Sep 17 00:00:00 2001
+From: Vasantha Ganesh K <vasanthaganesh.k@tuta.io>
+Date: Thu, 22 Jun 2017 23:38:40 +0530
+Subject: [PATCH] removed `check-conventions' from make
+
+---
+ Makefile                          |   7 +-
+ tests/haskell-code-conventions.el | 165 ------------------------------
+ 2 files changed, 1 insertion(+), 171 deletions(-)
+ delete mode 100644 tests/haskell-code-conventions.el
+
+diff --git a/Makefile b/Makefile
+index b2c89d6..aa907c5 100644
+--- a/Makefile
++++ b/Makefile
+@@ -79,12 +79,7 @@ build-$(EMACS_VERSION)/build-flag : build-$(EMACS_VERSION) $(patsubst %.el,build
+ check-%: tests/%-tests.el
+ 	$(BATCH) -l "$<" -f ert-run-tests-batch-and-exit;
+ 
+-check: compile $(AUTOLOADS) check-ert check-conventions
+-
+-check-conventions :
+-	$(BATCH) -l tests/haskell-code-conventions.el                                           \
+-                 -f haskell-check-conventions-batch-and-exit
+-	@echo "conventions are okay"
++check: compile $(AUTOLOADS) check-ert
+ 
+ check-ert: $(ELCHECKS)
+ 	$(BATCH) --eval "(when (= emacs-major-version 24)					\
+-- 
+2.18.0
+