"Section 7 of GPLv3 explicitly allows copyright holders to
exempt recipients of the software from specific terms of the
license. Interestingly, people who redistribute the software have
the option of removing those added permissions. The new GCC runtime
library license is GPLv3, but with an additional permission as
described in Section 7. That permission reads:
"You have permission to propagate a work of Target Code formed
by combining the Runtime Library with Independent Modules, even if
such propagation would otherwise violate the terms of GPLv3,
provided that all Target Code was generated by Eligible Compilation
Processes. You may then convey such a combination under terms of
your choice, consistent with the licensing of the Independent
Modules.
"Anybody who distributes a program which uses the GCC runtime,
and which is not licensed under GPLv3, will depend on this
exemption, so it is good to understand what it says. In short, it
allows the runtime to be combined with code under any license as
long as that code has been built with an "Eligible Compilation
Process."