[Polly][CI] Unconditionally delete test-suite build

The test-suite should be recompiled every time, even in incremental
builds.

.ci/buildbot/worker.py

@@ -291,6 +291,10 @@ class Worker:
         """Convenience wrapper for rmtree()"""
         return rmtree(*args, *kwargs)
 
+    def try_delete(self, *args, **kwargs):
+        """Convenience wrapper for try_delete()"""
+        return try_delete(*args, *kwargs)
+
     def checkout(self, giturl, sourcepath):
         """Convenience wrapper for checkout()"""
         return checkout(giturl, sourcepath)

polly/ci/polly-x86_64-linux-test-suite.py

@@ -50,6 +50,9 @@ with worker.run(
     with w.step("checkout-testsuite", halt_on_fail=True):
         w.checkout("https://github.com/llvm/llvm-test-suite", testsuitesrcdir)
 
+    with w.step("clean-testsuite"):
+        w.try_delete(testsuitebuilddir)
+
     with w.step("configure-testsuite", halt_on_fail=True):
         jobsarg = f";-j{w.jobs}" if w.jobs else ""
         w.run_command(