Use a common header file for Windows errno names.

In earlier Visual Studio and MinGW editions, BSD socket errno:s were
left undefined. This is no longer the case. This may cause build or
runtime errors. To avoid this, we are using a common header file which
corrects all definitions. This header will also be used with other
projects such as sercd, unfs3, PulseAudio etc.
diff --git a/common/rdr/FdInStream.cxx b/common/rdr/FdInStream.cxx
index adb14c5..22433a1 100644
--- a/common/rdr/FdInStream.cxx
+++ b/common/rdr/FdInStream.cxx
@@ -31,8 +31,7 @@
 #define close closesocket
 #undef errno
 #define errno WSAGetLastError()
-#undef EINTR
-#define EINTR WSAEINTR
+#include <os/winerrno.h>
 #else
 #include <sys/types.h>
 #include <errno.h>