kbuild: fix UML build error with CONFIG_GCC_PLUGINS

UML fails to build with CONFIG_GCC_PLUGINS=y.

$ make -s ARCH=um mrproper
$ make -s ARCH=um allmodconfig
$ make ARCH=um
  UPD     include/generated/uapi/linux/version.h
  WRAP    arch/x86/include/generated/uapi/asm/bpf_perf_event.h
  WRAP    arch/x86/include/generated/uapi/asm/poll.h
  WRAP    arch/x86/include/generated/asm/dma-contiguous.h
  WRAP    arch/x86/include/generated/asm/early_ioremap.h
  WRAP    arch/x86/include/generated/asm/export.h
  WRAP    arch/x86/include/generated/asm/mcs_spinlock.h
  WRAP    arch/x86/include/generated/asm/mm-arch-hooks.h
  SYSTBL  arch/x86/include/generated/asm/syscalls_32.h
  SYSHDR  arch/x86/include/generated/asm/unistd_32_ia32.h
  SYSHDR  arch/x86/include/generated/asm/unistd_64_x32.h
  SYSTBL  arch/x86/include/generated/asm/syscalls_64.h
  SYSHDR  arch/x86/include/generated/uapi/asm/unistd_32.h
  SYSHDR  arch/x86/include/generated/uapi/asm/unistd_64.h
  SYSHDR  arch/x86/include/generated/uapi/asm/unistd_x32.h
  HOSTCC  scripts/unifdef
  CC      arch/x86/um/user-offsets.s
cc1: error: cannot load plugin ./scripts/gcc-plugins/cyc_complexity_plugin.so
./scripts/gcc-plugins/cyc_complexity_plugin.so: cannot open shared object file: No such file or directory
cc1: error: cannot load plugin ./scripts/gcc-plugins/structleak_plugin.so
./scripts/gcc-plugins/structleak_plugin.so: cannot open shared object file: No such file or directory
cc1: error: cannot load plugin ./scripts/gcc-plugins/latent_entropy_plugin.so
./scripts/gcc-plugins/latent_entropy_plugin.so: cannot open shared object file: No such file or directory
cc1: error: cannot load plugin ./scripts/gcc-plugins/randomize_layout_plugin.so
./scripts/gcc-plugins/randomize_layout_plugin.so: cannot open shared object file: No such file or directory
make[1]: *** [scripts/Makefile.build;119: arch/x86/um/user-offsets.s] Error 1
make: *** [arch/um/Makefile;152: arch/x86/um/user-offsets.s] Error 2

Reorder the preparation stage (with cleanups) to make sure gcc-plugins
is built before descending to arch/x86/um/.

Fixes: 6b90bd4ba4 ("GCC plugin infrastructure")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -1110,9 +1110,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h
 
 macroprepare: prepare1 archmacros
 
-archprepare: archheaders archscripts macroprepare scripts_basic
+archprepare: archheaders archscripts macroprepare scripts_basic gcc-plugins
 
-prepare0: archprepare gcc-plugins
+prepare0: archprepare
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..

arch/um/Makefile

@@ -116,7 +116,8 @@ endef
 archheaders:
 	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) asm-generic archheaders
 
-archprepare: include/generated/user_constants.h
+archprepare:
+	$(Q)$(MAKE) $(build)=$(HOST_DIR)/um include/generated/user_constants.h
 
 LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
 LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
@@ -146,25 +147,4 @@ archclean:
 	@find . \( -name '*.bb' -o -name '*.bbg' -o -name '*.da' \
 		-o -name '*.gcov' \) -type f -print | xargs rm -f
 
-# Generated files
-
-$(HOST_DIR)/um/user-offsets.s: __headers FORCE
-	$(Q)$(MAKE) $(build)=$(HOST_DIR)/um $@
-
-define filechk_gen-asm-offsets
-        (set -e; \
-         echo "/*"; \
-         echo " * DO NOT MODIFY."; \
-         echo " *"; \
-         echo " * This file was generated by arch/$(ARCH)/Makefile"; \
-         echo " *"; \
-         echo " */"; \
-         echo ""; \
-         sed -ne "/^->/{s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; s:->::; p;}" < $<; \
-         echo ""; )
-endef
-
-include/generated/user_constants.h: $(HOST_DIR)/um/user-offsets.s
-	$(call filechk,gen-asm-offsets)
-
 export HEADER_ARCH SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS DEV_NULL_PATH

arch/x86/um/Makefile

@@ -36,10 +36,12 @@ subarch-$(CONFIG_MODULES) += ../kernel/module.o
 
 USER_OBJS := bugs_$(BITS).o ptrace_user.o fault.o
 
-extra-y += user-offsets.s
 $(obj)/user-offsets.s: c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) \
 	-Iarch/x86/include/generated
 
+include/generated/user_constants.h: $(obj)/user-offsets.s
+	$(call filechk,offsets,__USER_CONSTANT_H__)
+
 UNPROFILE_OBJS := stub_segv.o
 CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)