[pie_flavor]

If the project is licensed under the GPL, all the code in it is licensed under the GPL. The author is not precluded from later relicensing the non-GPL portions of the project under a different license - it's their code, they can release it under whatever license they want - but there will always be a version of that code that is under the GPL.

[pclmulqdq]

This is true, but if you dual license like this, your code will also carry another more permissive license, like Apache, BSD, or MIT, without an explicit re-licensing at a later date. It (that code only) can then be used under the more permissive license straight from the GPL-marked project. To convert from a GPL-licensed project, the user would only have to replace the GPL-licensed components.