From the gnulib commit log:
commit
e2646b0c6b5acda25e9ffeb4c12a5513a1e3b5ac
Author: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri Jun 27 11:35:44 2014 -0700
mktime: merge #if/#ifdef usage from glibc
* lib/mktime.c: Use "#if defined DEBUG && DEBUG", not "#if DEBUG",
as that works with both Glibc's and Gnulib's style.
See thread starting at Siddhesh Poyarekar's bug report at:
http://lists.gnu.org/archive/html/bug-gnulib/2014-06/msg00102.html
+2014-06-28 Paul Eggert <eggert@cs.ucla.edu>
+
+ mktime: merge #if/#ifdef usage from glibc
+ * lib/mktime.c: Use "#if defined DEBUG && DEBUG", not "#if DEBUG",
+ as that works with both Glibc's and Gnulib's style.
+ See thread starting at Siddhesh Poyarekar's bug report at:
+ http://lists.gnu.org/archive/html/bug-gnulib/2014-06/msg00102.html
+
2014-06-28 Siddhesh Poyarekar <siddhesh@redhat.com>
* sysdeps/generic/memcopy.h: Define MEMCPY_OK_FOR_FWD_MEMMOVE.
#include <string.h> /* For the real memcpy prototype. */
-#if DEBUG
+#if defined DEBUG && DEBUG
# include <stdio.h>
# include <stdlib.h>
/* Make it work even if the system's libc has its own mktime routine. */
libc_hidden_weak (timelocal)
#endif
\f
-#if DEBUG
+#if defined DEBUG && DEBUG
static int
not_equal_tm (const struct tm *a, const struct tm *b)