Use if_changed_rule so rule_cc_o_c runs cmd_save_c_flags for the kunit objects. Without the saved flags CONFIG_LTO_CLANG_THIN_DIST runs the ThinLTO backend with no --target and generates x86_64 code from arm64 bitcode. Fixes: 1dd4187f53c3 ("iommupt: Add a kunit test for Generic Page Table") Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202610110841.120JzAJG-lkp@intel.com/ Assisted-by: LLM Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>