clar: compilation fix for GNU/Hurd

clar.h fails to define CLAR_MAX_PATH on GNU/Hurd where PATH_MAX is
not defined.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sthibaul

t/unit-tests/clar/clar.h

@@ -10,7 +10,7 @@
 #include <stdlib.h>
 #include <limits.h>
 
-#if defined(_WIN32) && defined(CLAR_WIN32_LONGPATHS)
+#if defined(__GNU__) || defined(_WIN32) && defined(CLAR_WIN32_LONGPATHS)
 # define CLAR_MAX_PATH 4096
 #elif defined(_WIN32)
 # define CLAR_MAX_PATH MAX_PATH