[PowerPC] PPC LLD buildbot test instability fix.

[stefanp]

Summary

The LLD buildbot has some tests that are not reliable.
Hopefully reducing the number of threads for the test will fix the issue.

[gkistanova]

Looks like you are shooting in the dark, frankly.
But adding verbosity to LIT should help troubleshooting at least.
Please feel free to commit.

[stefanp]

@gkistanova
Thank you for the review Galina.
I unfortunately don't have commit access to Zorg. Could you commit this for me?

[stefanp]

Thank you Galina!
Committed at r371652.

buildbot/osuosl/master/config/builders.py

return [
          'factory': LLDPerformanceTestsuite.getFactory(targets=["bin/lld"]),
          'category'   : 'lld'},
 
         {'name' : "ppc64le-lld-multistage-test",
          'slavenames' : ["ppc64le-lld-multistage-test"],
          'builddir' : "ppc64le-lld-multistage-test",
          'factory': UnifiedTreeBuilder.getCmakeWithNinjaMultistageBuildFactory(
                                     extra_configure_args=[
-                                        '-DLLVM_ENABLE_ASSERTIONS=ON'],
+                                        '-DLLVM_ENABLE_ASSERTIONS=ON',
+                                        '-DLLVM_LIT_ARGS="-sv --threads=10"'],
                                     depends_on_projects=['llvm', 'clang', 'lld']),
          'category'   : 'lld'},
 
         {'name' : "lld-x86_64-ubuntu-fast",
          'slavenames' : ["as-builder-4"],
          'builddir' : "lld-x86_64-ubuntu-fast",
          'mergeRequests': False,
          'factory': UnifiedTreeBuilder.getCmakeWithNinjaBuildFactory(