[clang] set python3 as required build dependency

[Avimitin]

Summary

The required HTMLLogger include file needs python3 to run resource_bundle.py to bundle all the html/css/js resources. However, if user sets -DLLVM_INCLUDE_TESTS=OFF, CMake will not find python3 and the resource bundler will never be executed. This patch set the python3 as a required build dependency to fix this problem.

[phosek]

LGTM

[Avimitin]

I can't commit this change myself, please help me commit this, thank you.

clang/CMakeLists.txt

if(CLANG_BUILT_STANDALONE)
 
   include_directories(${LLVM_INCLUDE_DIRS})
   link_directories("${LLVM_LIBRARY_DIR}")
 
   set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin )
   set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
   set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
 
-  if(LLVM_INCLUDE_TESTS)
-    find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION} REQUIRED
-      COMPONENTS Interpreter)
 
+  if(LLVM_INCLUDE_TESTS)
     # Check prebuilt llvm/utils.
     if(EXISTS ${LLVM_TOOLS_BINARY_DIR}/FileCheck${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/count${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/not${CMAKE_EXECUTABLE_SUFFIX})
       set(LLVM_UTILS_PROVIDED ON)
     endif()
 
     # Seek installed Lit.