Disable LLVMBuild.txt dependencies and DummyConfigureOutput writing for official builds (#3319)

utils/llvm-build/llvmbuild/main.py

@@ -554,6 +554,8 @@ subdirectories = %s
 #
 # FIXME: File a CMake RFE to get a properly supported version of this
 # feature.
+
+if(NOT HLSL_OFFICIAL_BUILD)
 """)
         for dep in dependencies:
             f.write("""\
@@ -561,6 +563,10 @@ configure_file(\"%s\"
                ${CMAKE_CURRENT_BINARY_DIR}/DummyConfigureOutput)\n""" % (
                 cmake_quote_path(dep),))
 
+        f.write("""
+endif(NOT HLSL_OFFICIAL_BUILD)
+""")
+
         # Write the properties we use to encode the required library dependency
         # information in a form CMake can easily use directly.
         f.write("""