gnu: git: Define ‘PATH_MAX’ on GNU/Hurd.

Fixes a regression introduced in 04e9e4a462.

* gnu/packages/patches/git-clar-path-max.patch: New file.
* gnu/packages/version-control.scm (git-minimal): Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

Change-Id: I7b1eb519952674cf66b745bd0a71bbe3395d3bdc

gnu/local.mk

@@ -1439,6 +1439,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/ghostscript-no-header-creationdate.patch \
   %D%/packages/patches/gimp-fix-metadata-editor.patch		\
   %D%/packages/patches/gimp-fix-tiff-load.patch			\
+  %D%/packages/patches/git-clar-path-max.patch			\
   %D%/packages/patches/git-filter-repo-generate-doc.patch	\
   %D%/packages/patches/gklib-suitesparse.patch			\
   %D%/packages/patches/glib-appinfo-watch.patch			\

gnu/packages/patches/git-clar-path-max.patch

@@ -0,0 +1,16 @@
+On GNU/Hurd, 'PATH_MAX' is undefined.  Provide a reasonable default value.
+Adapted from <https://github.com/libgit2/libgit2/pull/7100>.
+
+diff --git a/tests/clar/clar.h b/tests/clar/clar.h
+index ca72292ae91..98e2b14e880 100644
+--- a/t/unit-tests/clar/clar.h
++++ b/t/unit-tests/clar/clar.h
+@@ -14,6 +14,8 @@
+ # define CLAR_MAX_PATH 4096
+ #elif defined(_WIN32)
+ # define CLAR_MAX_PATH MAX_PATH
++#elif !defined(PATH_MAX)			  /* GNU/Hurd */
++# define CLAR_MAX_PATH 4096
+ #else
+ # define CLAR_MAX_PATH PATH_MAX
+ #endif

gnu/packages/version-control.scm

@@ -320,7 +320,8 @@ Python 3.3 and later, rather than on Python 2.")
                                   version ".tar.xz"))
               (sha256
                (base32
-                "1ifpkrr64g8b0vv13155gz876s2f4vcqrvhgc75lkab9dzlgxn1w"))))
+                "1ifpkrr64g8b0vv13155gz876s2f4vcqrvhgc75lkab9dzlgxn1w"))
+              (patches (search-patches "git-clar-path-max.patch"))))
     (build-system gnu-build-system)
     (arguments
      (list