bug#19909: [PATCH] Error out if with-file-notification=w32 is specified on cygwin

[Robert Pluim]

It's a combination that won't compile, so it's probably best to error
out during configure.

diff --git a/ChangeLog b/ChangeLog
index 4365668..dec9ce0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-20  rpluim  <rpluim@gmail.com>
+
+       * configure.ac: Error out if with-file-notification=w32 is
+       specified on cygwin.
+
 2015-02-13  Jan Djärv  <jan.h.d@swipnet.se>
 
        * configure.ac: Set locallisppath to empty for NS self contained,
diff --git a/configure.ac b/configure.ac
index 0bcc55c..048168a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2659,6 +2659,10 @@ fi
 
 dnl MS Windows native file monitor is available for mingw32 only.
 case $with_file_notification,$opsys in
+  w32,cygwin)
+    AC_MSG_ERROR([`--with-file-notification=w32' was specified, but
+    this is only supported on MS-Windows native and MinGW32 builds])
+    ;;
   w32,* | yes,mingw32)
     AC_CHECK_HEADER(windows.h)
     if test "$ac_cv_header_windows_h" = yes ; then