[PATCH RFC] CYGWIN: avoid implicit declaration warning

["Torsten Bögershausen" <tboegi@web.de>]

gcc under cygwin reports several warnings like this:
 warning: implicit declaration of function 'memmem'
  [-Wimplicit-function-declaration]
This has been observed under CYGWIN-32 with GCC 4.7.3 as well
as CYGWIN-64 with gcc v4.8.3-5 x86-64

Do not #define _XOPEN_SOURCE 600 for CYGWIN.

Reported-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
---
This may be a start for a patch, tested under CYGWIN-32,
both Windows7 and XP
 git-compat-util.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index 400e921..cef2691 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -75,7 +75,8 @@
 # endif
 #elif !defined(__APPLE__) && !defined(__FreeBSD__) && !defined(__USLC__) && \
       !defined(_M_UNIX) && !defined(__sgi) && !defined(__DragonFly__) && \
-      !defined(__TANDEM) && !defined(__QNX__) && !defined(__MirBSD__)
+      !defined(__TANDEM) && !defined(__QNX__) && !defined(__MirBSD__) && \
+      !defined(__CYGWIN__)
 #define _XOPEN_SOURCE 600 /* glibc2 and AIX 5.3L need 500, OpenBSD needs 600 for S_ISLNK() */
 #define _XOPEN_SOURCE_EXTENDED 1 /* AIX 5.3L needs this */
 #endif
-- 
1.9.1.dirty