[zorg] [PowerPC] Limit number of threads to 20 on clang-ppc64le-rhel buildbot

[saghir]

Summary

Earlier, we reduced the number of threads to 64 but we were still seeing
sanitizer tests failing. We experimented with the number of threads and saw
20 threads working fine for the bot. This patch reduces the number of threads
from 64 to 20 on the clang-ppc64le-rhel buildbot.

[nemanjai]

LGTM. Let's reduce this until we can add the option to limit the number of threads for LLD into lit configs.

[nemanjai]

Forgot to accept.

[saghir]

Updating number of threads to 20.

buildbot/osuosl/master/config/builders.py

return [
                                                             stage1_config='Release',
                                                             nt_flags=['--threads=16', '--build-threads=16'],
                                                             extra_cmake_args=["-DLLVM_ENABLE_ASSERTIONS=On", "-DCMAKE_C_COMPILER=clang",
                                                                               "-DCMAKE_CXX_COMPILER=clang++",
                                                                               "-DCLANG_DEFAULT_LINKER=lld",
                                                                               "-DCMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/opt/rh/devtoolset-7/root/usr",
                                                                               "-DCMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/opt/rh/devtoolset-7/root/usr",
                                                                               "-DLLVM_BINUTILS_INCDIR=/usr/include", "-DBUILD_SHARED_LIBS=ON", "-DLLVM_ENABLE_WERROR=ON",
-                                                                              "-DLLVM_LIT_ARGS='-vj 64'"]),
+                                                                              "-DLLVM_LIT_ARGS='-vj 20'"]),
          'category' : 'clang'},
 
         {'name': "clang-s390x-linux",
          'slavenames':["systemz-1"],
          'builddir':"clang-s390x-linux",
          'factory' : ClangBuilder.getClangCMakeBuildFactory(jobs=4,
                                                             clean=False,
                                                             checkout_lld=False,