Avoid including pipe stream headers when streams are disabled.

Fixes compilation with wxUSE_STREAMS==0.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74529 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/unix/execute.h

@@ -15,8 +15,10 @@
 #include "wx/hashmap.h"
 #include "wx/process.h"
 
+#if wxUSE_STREAMS
     #include "wx/unix/pipe.h"
     #include "wx/private/streamtempinput.h"
+#endif
 
 class wxEventLoopBase;