only require mkisofs if isofs root is actually selected

SVN-Revision: 9211

target/linux/x86/Makefile

@@ -19,6 +19,6 @@ DEFAULT_PACKAGES += kmod-natsemi kmod-ne2k-pci
 $(eval $(call Target,generic))
 $(eval $(call Target,mediacenter))
 $(eval $(call BuildTarget))
-$(eval $(call RequireCommand,mkisofs, \
+$(eval $(call $(if $(CONFIG_TARGET_ROOTFS_ISO),RequireCommand,Ignore),mkisofs, \
    	Please install mkisofs. \
 ))