* 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/pipe.cc

@@ -12,6 +12,7 @@ details. */
 #include <unistd.h>
 #include <sys/fcntl.h>
 #include <errno.h>
+#include "dtable.h"
 
 static int
 make_pipe (int fildes[2], unsigned int psize, int mode)