Assert that wxEXEC_SYNC is not passed in flags to wxProcess::Open

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@16182 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/process.tex

@@ -212,7 +212,8 @@ exits to avoid memory leaks.
 \wxheading{Parameters}
 
 \docparam{cmd}{The command to execute, including optional arguments.}
-\docparam{flags}{The flags to pass to \helpref{wxExecute}{wxexecute}.}
+\docparam{flags}{The flags to pass to \helpref{wxExecute}{wxexecute}.
+  NOTE: wxEXEC_SYNC should not be used.}
 
 \wxheading{Return value}