gnu: plotutils: Fix build on non-x86_64 architectures.

* gnu/packages/patches/plotutils-spline-test.patch: Add patch.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/plotutils.scm (plotutils)[patches]: Apply it.

gnu/local.mk

@@ -1408,6 +1408,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/plink-endian-detection.patch		\
   %D%/packages/patches/plib-CVE-2011-4620.patch		\
   %D%/packages/patches/plib-CVE-2012-4552.patch		\
+  %D%/packages/patches/plotutils-spline-test.patch		\
   %D%/packages/patches/podofo-cmake-3.12.patch			\
   %D%/packages/patches/portaudio-audacity-compat.patch		\
   %D%/packages/patches/portmidi-modular-build.patch		\

gnu/packages/patches/plotutils-spline-test.patch

@@ -0,0 +1,34 @@
+Description: Work around i386 testsuite error
+Author: Andreas Metzler <ametzler@debian.org>
+Origin: vendor
+Bug: http://lists.gnu.org/archive/html/bug-plotutils/2017-02/msg00001.html
+Bug-Debian: https://bugs.debian.org/856134
+Forwarded: http://lists.gnu.org/archive/html/bug-plotutils/2017-02/msg00002.html
+Last-Update: 2017-02-25
+
+--- a/test/spline.test
++++ b/test/spline.test
+@@ -3,12 +3,21 @@
+ echo 0 1 0.5 0.75 -0.25 0 | ../spline/spline -a -T 1 -n 120 \
+ 	--precision 5 -p >spline.out
+ 
++# Work around testsuite error
++# http://lists.gnu.org/archive/html/bug-plotutils/2016-04/msg00000.html
++#
+ # work around line end problems in installations with DJGPP under DOS
+-tr -d '\015' < spline.out > spline.dos
++tr -d '\015' < spline.out \
++	| head -n 120 | tail -n 119 \
++	> spline.dos
+ 
+-if cmp -s $SRCDIR/spline.xout spline.dos
++# cannot patch spline.xout, it is used as input for graph.test.
++head -n 120 $SRCDIR/spline.xout | tail -n 119 > spline.xout.4comp
++
++if cmp -s spline.xout.4comp spline.dos
+ 	then retval=0;
+ 	else retval=1;
+ 	fi;
+ 
++rm -f spline.xout.4comp
+ exit $retval

gnu/packages/plotutils.scm

@@ -73,7 +73,12 @@
                  (substitute* "libplot/z_write.c"
                    (("png_ptr->jmpbuf")
                     "png_jmpbuf (png_ptr)"))
-                 #t))))
+                 #t))
+             (patches
+              ;; The test suite fails on some architectures such as i686 (see:
+              ;; https://lists.gnu.org/archive/html/bug-plotutils/2016-04/msg00002.html).
+              ;; The following Debian patch works around it.
+              (search-patches "plotutils-spline-test.patch"))))
     (build-system gnu-build-system)
     (arguments
      `(#:configure-flags (list "--enable-libplotter")))