[9.0.0 Release] One week to the branch

Hello everyone,

This is a reminder that the upcoming release branch is scheduled for
one week from today, on Thursday 18 July 2019.

The full schedule can be found under "Upcoming Releases" in the column
to the right at https://llvm.org

Please try to avoid committing majorly disruptive changes just before
or after the branch.

As the branch is created, the trunk version will become 10.0.0.