* winsup.h: Split out dtable definitions into separate header file.

* dtable.h: New file.
* sigproc.h: Eliminate pinfo.h usage here.  Use it in source files that need
it.

winsup/cygwin/fhandler_serial.cc

@@ -13,6 +13,7 @@ details. */
 #include <errno.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include "pinfo.h"
 
 /**********************************************************************/
 /* fhandler_serial */