cygwin: allow pushing to UNC paths

 cygwin can use an UNC path like //server/share/repo

 $ cd //server/share/dir
 $ mkdir test
 $ cd test
 $ git init --bare

 However, when we try to push from a local Git repository to this repo,
 there is a problem: Git converts the leading "//" into a single "/".

 As cygwin handles an UNC path so well, Git can support them better:

 - Introduce cygwin_offset_1st_component() which keeps the leading "//",
   similar to what Git for Windows does.

 - Move CYGWIN out of the POSIX in the tests for path normalization in t0060

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-compat-util.h b/git-compat-util.h
index 199042a..59866d7 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -189,6 +189,9 @@
 #include <sys/sysctl.h>
 #endif
 
+#if defined(__CYGWIN__)
+#include "compat/cygwin.h"
+#endif
 #if defined(__MINGW32__)
 /* pull in Windows compatibility stuff */
 #include "compat/mingw.h"