[uml-devel] uml-2.5.39 build fixes

[James M. <jam...@ho...>]

This updates ARCH_SUBDIRS to have the missing trailing / so it can be added
to core-y directly and gets rid of the old link.ld references.  ARCH_SUBDIRS
is used in the for loops in the Makefile to clean up.

It also drops the core-y from Makefile-os-Linux since this is already
included from the arch/um/Makefile anyway and produced errors during build.
Do you want to get rid of the Makefile-os-Linux? or maybe the references in
Makefile

It puts in the user_syms.o that keeps escaping from arch/um/kernel/Makefile
which is seen as bad depmod/link problems with the standard library
funcitions.