1. Remove all the special handling of variables (-d -p -P -s -S) that
  were dealing with DBG (-d) LDSTATIC/NOPIE (-p), and the rest with
  disabling/enabling sanitizers.
2. Use emalloc/estrdup for all the allocators instead of only some cases.
3. Add -V varspec which passes variables on the command line (as DBG
  and LDSTATIC used to be passed before) instead of appending them
  to the on-the-fly Makefile using -v varspec.
4. Change the distrib and rescue Makefiles to use -V instead of the removed
  flags.

The motivation of this is to make variable handling consistent, less magical,
and remove the need for changing crunchgen each time we want to add disabling
an option by default.

(as proposed in tech-toolchain)

(christos)