lmb: only force on arches that use it

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/lib_generic/Makefile b/lib_generic/Makefile
index 4b8ed3a..4e4496a 100644
--- a/lib_generic/Makefile
+++ b/lib_generic/Makefile
@@ -38,7 +38,7 @@
 COBJS-y += display_options.o
 COBJS-y += div64.o
 COBJS-y += gunzip.o
-COBJS-y += lmb.o
+COBJS-$(CONFIG_LMB) += lmb.o
 COBJS-y += ldiv.o
 COBJS-$(CONFIG_MD5) += md5.o
 COBJS-y += net_utils.o