Support asdf's static-image-op.

* src/lisp/GNUMakefile
    * Don't add exec-final.o to lisp.a.  (But still remove exec-init.o
      from it.)
* src/tools/linker.sh
    * When linking the executable, need to link exec-final.o too.
* bin/make-main-dist.sh
    * Need to install exec-init.o and exec-final.o.  exec-init.o is
      needed to link a normal lisp; exec-final.o is used for the
      executable image.
    * Fix modes on some installed files.  exec-init.o, exec-final.o,
      and lisp.a don't need to be executable.