um: most of the SUBARCH uses can be killed

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[richard@nod.at: Re-export SUBARCH in arch/um/Makefile]
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/Makefile b/arch/um/Makefile
index 28688e6..4c993c8 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -50,7 +50,7 @@
 #
 # These apply to USER_CFLAGS to.
 
-KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ -DSUBARCH=\"$(SUBARCH)\" \
+KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
 	$(ARCH_INCLUDE) $(MODE_INCLUDE) -Dvmap=kernel_vmap	\
 	-Din6addr_loopback=kernel_in6addr_loopback \
 	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
@@ -99,7 +99,7 @@
 
 archheaders:
 	$(Q)$(MAKE) -C '$(srctree)' KBUILD_SRC= \
-		ARCH=$(SUBARCH) O='$(objtree)' archheaders
+		ARCH=$(HEADER_ARCH) O='$(objtree)' archheaders
 
 archprepare: include/generated/user_constants.h