Fix treatment of ld's nocombreloc option

Fix treatment of ld's nocombreloc option

* configure.ac (LDFLAGS_NOCOMBRELOC): New variable.
(LDFLAGS): Move nocombreloc option from here...
(LD_SWITCH_SYSTEM_TEMACS): ... to here.
This is an essential option that should not be in LDFLAGS,
because the user may override that at build time; eg
http://bugs.debian.org/684788.  temacs is the only thing
that actually needs this option; this is where it was orginally:
http://lists.gnu.org/archive/html/emacs-pretest-bug/2004-03/msg00170.html