IO.h uses ostream, sstream without including their headers

pkgsrc has a patch by Jörg Sonnenberger joerg@NetBSD.org which adds the includes of ostream and sstream to Eigen/src/Core/IO.h

The file uses ostream from the ostream header and stringstream from the sstream header, so arguably, the headers should be included.

Patch:

--- Eigen/src/Core/IO.h.orig    2020-04-18 02:56:39.805274318 +0000
+++ Eigen/src/Core/IO.h
@@ -11,6 +11,9 @@
 #ifndef EIGEN_IO_H
 #define EIGEN_IO_H
 
+#include <ostream>
+#include <sstream>
+
 namespace Eigen { 
 
 enum { DontAlignCols = 1 };