[libc] Add a new suite called "libc-long-running-tests".

This suite is helpful is adding long running tests which take a long
time to finish that they can be run on the public builders. They
will probably be run on special builders in future.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D104816

GitOrigin-RevId: 5e147d3058a0a01c19c83d322bef50bdaf8873ee
2 files changed