Windows: add missing definition of ENOTSOCK

The previous commit introduced the first use of ENOTSOCK. This macro is
not available on Windows. Define it as WSAENOTSOCK because that is the
corresponding error value reported by the Windows versions of socket
functions.
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

compat/mingw.h

@@ -73,6 +73,9 @@ typedef int pid_t;
 #ifndef ECONNABORTED
 #define ECONNABORTED WSAECONNABORTED
 #endif
+#ifndef ENOTSOCK
+#define ENOTSOCK WSAENOTSOCK
+#endif
 
 struct passwd {
 	char *pw_name;