Enable clean step for AVX512 windows buildbot job (#59)

Signed-off-by: Xiaodong Li <[email protected]>

Author: DoyleLi

buildbot/osuosl/master/config/builders.py

@@ -839,7 +839,7 @@
                     vs="autodetect",
                     vs_target_arch='x64',
                     stage1_config='Debug',
-                    clean=False,
+                    clean=True,
                     checkout_clang_tools_extra=True,
                     checkout_compiler_rt=False,
                     checkout_lld=False,