Changing toolchains is a very rare occurrence because the subtle differences will almost always cause problems. When someone suggests changing toolchains, they owe everyone a VERY CONVINCING argument. After which the changed warnings will be the LEAST of your problems as you migrate.
Toolchain upgrades will cause new warnings to surface as the detection gets better. But you DO want to fix them, don't you? You ARE a professional, aren't you? You DO care about your product's quality, don't you?
After over a decade without werror, followed by a decade with werror, I'd take werror every time. Warnings exist for a reason, and in the case of C compilers, VERY GOOD reasons that you really should address.
At my workplace, we use werror, static analysis, various lints, detekt... everything that can issue warnings about your code quality. If any of them complain, you can't merge your PR, because we're professionals.