It turns out, this would actually be a no-op change.
Here are some findings we’ve found with @sam-mccall while digging deeper at it.
In theory XCode 9.3 comes with a clang that prints 9.1.0 in its version string [1], but our toolchain requirements check for 9.3.0.
Looking at the same table, the next version of apple clang string that’s available is 10.0.0. Hence 9.3.0 doesn’t exist, and our soft error has already been enforcing people to install at least apple clang 10.0.0 (or XCode 10.0).
So previous version bump actually bumped the requirement to apple clang 10.0.0 effectively. Hence changing the documentation and cmake files to mention 10.0.0 should just be an RFC. Therefore I’d suggest treating this as a “typo in the documentation” rather than waiting for some release cycles.