Piotr's patch was missing many occurences of size_t. So,

using std::size_t;
This is the only way that we can ensure QCC support in the long term without having to think about it everytime.

Eigen/Core

@@ -147,6 +147,10 @@ namespace Eigen {
 #include "src/Core/Part.h"
 #include "src/Core/CacheFriendlyProduct.h"
 
+// we use size_t frequently and we'll never remember to prepend it with std:: everytime just to
+// ensure QNX/QCC support
+using std::size_t;
+
 } // namespace Eigen
 
 #include "src/Core/util/EnableMSVCWarnings.h"