As I've looked, it's in section 4, paragraph d), choice 0) of the LGPL3 : "Convey the Minimal Corresponding Source under the terms of this License, and the Cor

As I've looked, it's in section 4, paragraph d), choice 0) of the LGPL3 : "Convey the Minimal Corresponding Source under the terms of this License, and the Corresponding Application Code in a form suitable for, and under terms that permit, the user to recombine or relink the Application with a modified version of the Linked Version to produce a modified Combined Work, in the manner specified by section 6 of the GNU GPL for conveying Corresponding Source." So not exactly the toolchain, but definitely allows reinstallation of upgraded libraries. I didn't know.