The optional "slimdebug" variant is now available for use in e32 builds.

This currently has an impact on RVCT-based e32 builds and, when applied,
calls to armcc in udeb compilation have the "--no_debug_macros" and
"--remove_unneeded_entities" options added; there is no change to the vanilla
urel compilation call in RVCT-based builds, nor to the compiler calls in
other e32 builds using other toolchains.

The net result of applying "slimdebug" is a general decrease in udeb object
and image sizes due to the removal of debug table entries and unused debug
information.

Examples of the variant's application are as follows:

sbs -c armv5.slimdebug
sbs -c armv6_udeb.slimdebug

