Merge branch 'rj/no-xopen-source-for-cygwin'

Avoid compilation warnings on recent gcc toolchain on Cygwin.

* rj/no-xopen-source-for-cygwin:
  git-compat-util.h: don't define _XOPEN_SOURCE on cygwin

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