Add ENV.refurbish_args helper

Rationale: our arg refurbishment is normally only turned on when
called via the `make` wrapper, for compatibility reasons. However,
there are numberous places we'd like this to be turned on elsewhere,
like software that builds via `python setup.py` where bad flags from
the system python can be pulled in.

This helper appends 'O' to CCCFG, which enables refurbishment for
all calls of the compiler shims.
ksh: use ENV.refurbish_args helper