Release notes for wfSuppressWarnings change I backported to 1.20

See gerrit change 44165. I did the same thing for 1.19, since
no one told me I did it wrong (yay!) now doing it for 1.20.

Using separate commit for release notes in order to use
cherry-pick for the actual commit. Have no idea if that is
important or not.

Change-Id: I5b28b78d161653ce7e8da37be50c406e992b7354