[clang] Move CLANG_BOOTSTRAP_CMAKE_ARGS above PASSTHROUGH_VARIABLES

[xinxinw1]

Summary

I want to pass some CMake cache files in CLANG_BOOTSTRAP_CMAKE_ARGS as -C <cache file>.cmake arguments. I want to be able to use the values of the bootstrap passthrough variables in the cache files, so the cache file arguments need to be after passthrough variables. This should be safe because the values of passthrough variables are all constants and can't refer to values in CLANG_BOOTSTRAP_CMAKE_ARGS.

[smeenai]

LGTM

clang/CMakeLists.txt

ExternalProject_Add(${NEXT_CLANG_STAGE}
     SOURCE_DIR ${CMAKE_SOURCE_DIR}
     STAMP_DIR ${STAMP_DIR}
     BINARY_DIR ${BINARY_DIR}
     EXCLUDE_FROM_ALL 1
     CMAKE_ARGS
                 # We shouldn't need to set this here, but INSTALL_DIR doesn't
                 # seem to work, so instead I'm passing this through
                 -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
-                ${CLANG_BOOTSTRAP_CMAKE_ARGS}
                 ${PASSTHROUGH_VARIABLES}
+                ${CLANG_BOOTSTRAP_CMAKE_ARGS}
                  -DCLANG_STAGE=${NEXT_CLANG_STAGE}
                 ${COMPILER_OPTIONS}
                 ${${CLANG_STAGE}_CONFIG}
                 ${${CLANG_STAGE}_TABLEGEN}
                 ${LTO_LIBRARY} ${verbose} ${PGO_OPT}
                 ${${CLANG_STAGE}_LINKER}
                 ${${CLANG_STAGE}_AR}
                 ${${CLANG_STAGE}_RANLIB}