Fix Cygwin TCP_NODELAY issue from Paul Chu & Freddie

documentation/RELEASE_NOTES.md

@@ -27,6 +27,7 @@ The following bugs/issues have fixes included in this release:
   Inaccessible CA servers on Windows
 - [github: 83](https://github.com/epics-base/epics-base/issues/83)
   osdTimeGetCurrent doesn't work for subprocess on macOS
+- Recent Cygwin build problem with a missing `TCP_NODELAY` declaration.
 
 ### Perl CA Bindings under Conda
 

modules/libcom/src/osi/os/cygwin32/osdSock.h

@@ -27,6 +27,9 @@
 #include <net/if.h>
 #include <netdb.h>
 #include <unistd.h> /* close() and others */
+#ifndef TCP_NODELAY
+#  include <netinet/tcp.h>
+#endif
 
 
 typedef int                     SOCKET;