gnu: libgit2: Work around test failures on 32-bit platforms.

* gnu/packages/patches/libgit2-oom-test.patch: New file.
* gnu/packages/version-control.scm (libgit2)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -876,6 +876,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libexif-CVE-2016-6328.patch		\
   %D%/packages/patches/libexif-CVE-2017-7544.patch		\
   %D%/packages/patches/libgit2-mtime-0.patch			\
+  %D%/packages/patches/libgit2-oom-test.patch			\
   %D%/packages/patches/libgdata-fix-tests.patch			\
   %D%/packages/patches/libgdata-glib-duplicate-tests.patch	\
   %D%/packages/patches/libgnome-encoding.patch			\

gnu/packages/patches/libgit2-oom-test.patch

@@ -0,0 +1,62 @@
+Fix a test failure on 32-bit platforms as reported
+at <https://github.com/libgit2/libgit2/issues/4868>.
+
+From 415a8ae9c9b6ac18f0524b6af8e58408b426457d Mon Sep 17 00:00:00 2001
+From: Edward Thomson <ethomson@edwardthomson.com>
+Date: Thu, 13 Sep 2018 13:27:07 +0100
+Subject: [PATCH] tests: don't run buf::oom on 32-bit systems
+
+On a 32-bit Linux systems, the value large enough to make malloc
+guarantee a failure is also large enough that valgrind considers it
+"fishy".  Skip this test on those systems entirely.
+---
+ tests/buf/oom.c | 14 +++++++++-----
+ 1 file changed, 9 insertions(+), 5 deletions(-)
+
+diff --git a/tests/buf/oom.c b/tests/buf/oom.c
+index 2741a8ddf2..ec3bad9979 100644
+--- a/tests/buf/oom.c
++++ b/tests/buf/oom.c
+@@ -11,12 +11,8 @@
+  */
+ #if defined(GIT_ARCH_64) && defined(__linux__)
+ # define TOOBIG 0x0fffffffffffffff
+-#elif defined(__linux__)
+-# define TOOBIG 0x0fffffff
+ #elif defined(GIT_ARCH_64)
+ # define TOOBIG 0xffffffffffffff00
+-#else
+-# define TOOBIG 0xffffff00
+ #endif
+ 
+ /**
+@@ -25,13 +21,18 @@
+  * will fail.  And because the git_buf_grow() wrapper always
+  * sets mark_oom, the code in git_buf_try_grow() will free
+  * the internal buffer and set it to git_buf__oom.
+- * 
++ *
+  * We initialized the internal buffer to (the static variable)
+  * git_buf__initbuf.  The purpose of this test is to make sure
+  * that we don't try to free the static buffer.
++ *
++ * Skip this test entirely on 32-bit platforms; a buffer large enough
++ * to guarantee malloc failures is so large that valgrind considers
++ * it likely to be an error.
+  */
+ void test_buf_oom__grow(void)
+ {
++#ifdef GIT_ARCH_64
+ 	git_buf buf = GIT_BUF_INIT;
+ 
+ 	git_buf_clear(&buf);
+@@ -40,6 +41,9 @@ void test_buf_oom__grow(void)
+ 	cl_assert(git_buf_oom(&buf));
+ 
+ 	git_buf_free(&buf);
++#else
++    cl_skip();
++#endif
+ }
+ 
+ void test_buf_oom__grow_by(void)

gnu/packages/version-control.scm

@@ -469,7 +469,8 @@ everything from small to very large projects with speed and efficiency.")
               (sha256
                (base32
                 "15kp4sq72kh762bm7dgspyrk0a6siarvll3k7nrhs0xy77idf80g"))
-              (patches (search-patches "libgit2-mtime-0.patch"))
+              (patches (search-patches "libgit2-mtime-0.patch"
+                                       "libgit2-oom-test.patch"))
 
               ;; Remove bundled software.
               (snippet '(begin