numfmt: improve processing throughput by 800%

numfmt: improve processing throughput by 800%

The devmsg() calls that took quote_n() arguments,
didn't normally output anything, but still incurred
the overhead of those quote_n() calls.

* src/numfmt.c (devmsg): Move the inline function
with _internal_ enablement check to...
* src/system.h: ...here as a variadic macro, with
the enablement check at the outer level.
* src/factor.c: As per numfmt.c but there is no
performance change in this case.
* NEWS: Mention the significant performance improvement.