_extra_flags_ = -fno-builtin -m64
-#We #undef __x86_64__ for kernelspace, not for userspace where
-#it's needed for headers to work!
-ARCH_KERNEL_DEFINES = -U__$(SUBARCH)__
KBUILD_CFLAGS += $(_extra_flags_)
-CHECKFLAGS += -m64
+CHECKFLAGS += -m64 -D__x86_64__
KBUILD_AFLAGS += -m64
LDFLAGS += -m elf_x86_64
KBUILD_CPPFLAGS += -m64