Fix parallel bootstrap on MS-Windows in lib/ and lisp/.

Fix parallel bootstrap on MS-Windows in lib/ and lisp/.

 lib/makefile.w32-in ($(GNULIBOBJS)): Depend on stamp_BLD.  This
 replaces separate dependency for each object file, which required
 the same object file to be mentioned twice, causing failures in
 parallel builds.
 lisp/makefile.w32-in (compile, compile-always): Depend on
 update-subdirs, not on subdirs.el.  Otherwise, several different
 sub-targets of 'bootstrap' running in parallel could
 simultaneously write to subdirs.el, producing a garbled file.