Fix -Wundef warning.  Addressed upstream as part of this commit:

commit 888c679ba406e89d86bdfbde033e307f5af5198f
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Jul 10 14:24:30 2014 +0530

    Sync up error.c with gnulib

diff --git a/misc/error.c b/misc/error.c
index 6fb192da4b38a4f9..3d0156e406fa1539 100644
--- a/misc/error.c
+++ b/misc/error.c
@@ -100,7 +100,7 @@ print_errno_message (int errnum)
 
 #if defined HAVE_STRERROR_R || _LIBC
   char errbuf[1024];
-# if STRERROR_R_CHAR_P || _LIBC
+# if _LIBC || STRERROR_R_CHAR_P
   s = __strerror_r (errnum, errbuf, sizeof errbuf);
 # else
   if (__strerror_r (errnum, errbuf, sizeof errbuf) == 0)