Turn on ccache and clean builds for llvm-clang-x86_64-sie-win builder

[dyung]

Summary

Ccache now seems to be working on Windows when building with ninja+VS, so enable it, and also switch to doing clean builds (although experience doesn't seem to suggest this is really necessary, it is a recommended practice, so we can see how much it affects the build times now that ccache is available.

On a test run on the buildbot, a clean build with 100% hit rate using ccache took about 85 seconds.

[gkistanova]

LGTM.

buildbot/osuosl/master/config/builders.py

# Clang builders.
     {'name' : "llvm-clang-x86_64-sie-win",
     'tags'  : ["llvm", "clang", "clang-tools-extra", "lld", "cross-project-tests"],
     'workernames' : ["sie-win-worker"],
     'builddir': "llvm-clang-x86_64-sie-win",
     'factory' : UnifiedTreeBuilder.getCmakeWithNinjaWithMSVCBuildFactory(
                     vs="autodetect",
                     target_arch='x64',
                     depends_on_projects=['llvm','clang','clang-tools-extra','lld','cross-project-tests'],
-                    clean=False,
+                    clean=True,
                     extra_configure_args=[
                         "-DCMAKE_BUILD_TYPE=Release",
                         "-DCLANG_ENABLE_ARCMT=OFF",
                         "-DCLANG_ENABLE_CLANGD=OFF",
+                        "-DLLVM_CCACHE_BUILD=ON",
                         "-DLLVM_DEFAULT_TARGET_TRIPLE=x86_64-sie-ps5",
                         "-DLLVM_INCLUDE_EXAMPLES=OFF",
                         "-DLLVM_TARGETS_TO_BUILD=X86",
                         "-DLLVM_VERSION_SUFFIX=",
                         "-DLLVM_BUILD_RUNTIME=OFF",
                         "-DLLVM_ENABLE_ASSERTIONS=ON",
                         "-DLLVM_LIT_ARGS=--verbose -j61",
                         "-DPYTHON_EXECUTABLE=C:\Python310\python.exe"])},