Earlier quoted context omitted.
You are correct in that the license is free, but it isn't a copyleft license. This is a purely political decision: RMS wants gcc not only to be free software but he also wants it to be unusable to create non-free derivatives thus making it an active tool in furthering free software. clang undermines this because you can create non-free software based on it thus making it a tool that can easily be used to restrict fre…
Interesting that allowing you to do whatever you want with a piece of software (e.g. selling non-free derivatives) is considered restricting freedom .
Interesting that preventing users from doing something with a bit of software (e.g. selling non-free derivatives) is considered restricting freedom.
Kind of self evident when stated from the users point of view really.