iommupt/kunit: Use if_changed_rule for the kunit

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: 1dd4187f53 ("iommupt: Add a kunit test for Generic Page Table")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Assisted-by: LLM
Signed-off-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>

drivers/iommu/generic_pt/fmt/Makefile

@@ -25,6 +25,6 @@ $(eval $(foreach fmt,$(iommu_pt_fmt-m),$(call create_format,$(fmt),m)))
 # with -DGENERIC_PT_KUNIT
 $(obj)/kunit_iommu_%.o: $(src)/iommu_%.c FORCE
 	$(call rule_mkdir)
-	$(call if_changed_dep,cc_o_c)
+	$(call if_changed_rule,cc_o_c)
 
 obj-$(CONFIG_IOMMU_PT_KUNIT_TEST) += $(IOMMU_PT_KUNIT_TEST)