[llvm] [polly] [Buildbot][Polly] Move polly-x86_64-linux-test-suite build instructions into main repository (PR #166809)

[Michael Kruse via llvm-commits]

Meinersbur wrote:

@jplehr First draft about the proposed move of the build instruction next to the CMake cache. I know you had an RFC where to locate the script, but I forgot where the location was. Will update after first feedback.

A test buildbot master is running here: http://meinersbur.de:8011/#/builders/143

https://github.com/llvm/llvm-project/pull/166809