um: fix linker script generation

while we can't just use -U$(SUBARCH), we still need to kill idiotic define
(implicit -Di386=1), both for SUBARCH=i386 and SUBARCH=x86/CONFIG_64BIT=n
builds.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/um/kernel/Makefile

@@ -5,7 +5,8 @@
 
 CPPFLAGS_vmlinux.lds := -DSTART=$(LDS_START)		\
                         -DELF_ARCH=$(LDS_ELF_ARCH)	\
-                        -DELF_FORMAT=$(LDS_ELF_FORMAT)
+                        -DELF_FORMAT=$(LDS_ELF_FORMAT)	\
+			$(LDS_EXTRA)
 extra-y := vmlinux.lds
 clean-files :=
 

arch/x86/Makefile.um

@@ -14,6 +14,9 @@ LINK-y			+= $(call cc-option,-m32)
 
 export LDFLAGS
 
+LDS_EXTRA		:= -Ui386
+export LDS_EXTRA
+
 # First of all, tune CFLAGS for the specific CPU. This actually sets cflags-y.
 include $(srctree)/arch/x86/Makefile_32.cpu