Add Python binary path to CMake arguments for the clang-ppc64le-linux…

… builder

LLVM now requires Python 3.6 which is not available in the official Ubuntu 16.04
repositories. This patch adds the path to a manually built Python 3.6 to the
CMake arguments of the clang-ppc64le-linux builder.

buildbot/osuosl/master/config/builders.py

@@ -603,7 +603,9 @@
                     checkout_lld=False,
                     useTwoStage=False,
                     stage1_config='Release',
-                    extra_cmake_args=["-DLLVM_ENABLE_ASSERTIONS=ON"])},
+                    extra_cmake_args=[
+                        "-DLLVM_ENABLE_ASSERTIONS=ON",
+                        "-DPYTHON_EXECUTABLE:FILEPATH=/usr/local/bin/python3"])},
 
     {'name' : "clang-ppc64le-rhel",
     'tags'  : ["clang", "ppc", "ppc64le"],