kbuild: um fix so it compile with generic asm-offsets.h support

um has it own set of files for asm-offsets. So for now the
gen-asm-offset macro is just duplicated in the um Makefile.

This may well be the final solution since um is a bit special compared
to other architectures - time will tell.

Also added a dummy arch/um/kernel/asm-offsets.h file to keep kbuild happy.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/um/Makefile

@@ -197,6 +197,22 @@ define filechk_umlconfig
 	sed 's/ CONFIG/ UML_CONFIG/'
 endef
 
+define filechk_gen-asm-offsets
+        (set -e; \
+         echo "#ifndef __ASM_OFFSETS_H__"; \
+         echo "#define __ASM_OFFSETS_H__"; \
+         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 ""; \
+         echo "#endif" )
+endef
+
 $(ARCH_DIR)/include/uml-config.h : include/linux/autoconf.h
 	$(call filechk,umlconfig)
 

arch/um/kernel/asm-offsets.c

+/* Dummy file to make kbuild happy - unused! */