The GPL is described as a 'highly viral' license (if an application contains code which is licensed under GPL, distribution requires open sourcing of the whole application).
Do I understand correctly that linking GPL code with closed source run-time libraries provided by many commercial integrated software development environments has the effect that no (external/public) distribution of the resulting application is possible, simply because the closed source run-time libraries are not under GPL?
It is a bit more nuanced than a straight up yes or no.
In general, it is correct that you must be able (and legally allowed) to distribute the source code of all libraries that are used in a program that contains GPL licensed code.
The nuance comes when dealing with GPL licensed code and libraries that are part of the core infrastructure of a computer (OS Kernel, windowing system, etc.) and libraries that implement a standard interface. Under GPL, those libraries are exempt from the viral nature of the GPL.
The standard libraries for the major programming languages are likely to be intended to fall under this exemption, so I wouldn't worry too much when using a piece of GPL code in your Windows application written using Visual Studio.
