gnu: 4store: Remove preprocessor directive.

* gnu/packages/databases.scm (4store): Add patch to remove preprocessor
  directive.
* gnu/packages/patches/4store-unset-preprocessor-directive.patch: New file.
* gnu/local.mk: Register patch.

gnu/local.mk

@@ -544,6 +544,7 @@ MODULES_NOT_COMPILED +=				\
 patchdir = $(guilemoduledir)/%D%/packages/patches
 dist_patch_DATA =						\
   %D%/packages/patches/4store-fix-buildsystem.patch		\
+  %D%/packages/patches/4store-unset-preprocessor-directive.patch	\
   %D%/packages/patches/a2ps-CVE-2001-1593.patch	\
   %D%/packages/patches/a2ps-CVE-2014-0466.patch	\
   %D%/packages/patches/abiword-explictly-cast-bools.patch	\

gnu/packages/databases.scm

@@ -125,7 +125,8 @@
       (file-name (string-append name "-" version ".tar.gz"))
       (sha256
        (base32 "004fmcf1w75zhc1x3zc6kc97j4jqn2v5nhk6yb3z3cpfrhzi9j50"))
-      (patches (list (search-patch "4store-fix-buildsystem.patch")))))
+      (patches (search-patches "4store-unset-preprocessor-directive.patch"
+                               "4store-fix-buildsystem.patch"))))
     (build-system gnu-build-system)
     (native-inputs
      `(("perl" ,perl)

gnu/packages/patches/4store-unset-preprocessor-directive.patch

@@ -0,0 +1,16 @@
+This patch removes the _XOPEN_SOURCE preprocessor directive as it does not seem to be needed.
+Setting it removes the definition of strdup, which is used in filter-datatypes.c.
+
+Patch by Roel Janssen <roel@gnu.org>
+*** a/src/frontend/filter-datatypes.c	1970-01-01 01:00:00.000000000 +0100
+--- b/src/frontend/filter-datatypes.c	2018-04-03 17:39:23.177905592 +0200
+***************
+*** 18,24 ****
+   *  Copyright (C) 2006 Steve Harris for Garlik
+   */
+  
+- #define _XOPEN_SOURCE
+  #include <stdlib.h>
+  #include <string.h>
+  #include <math.h>
+--- 18,23 ----