CDRIVER-4697: More efficient trace toggle

[Julia-Garland]

Updated:
if (MONGOC_TRACE_ENABLED)
to
if (MONGOC_TRACE_ENABLED && gLogTrace)
via _mongoc_log_trace_is_enabled which has the same logic.

[eramongodb]

Mild concern that moving the MONGOC_TRACE_ENABLED check into the function may impede the compiler's ability to deduce always-false conditions at usage sites. The original ticket description requested if (MONGOC_TRACE_ENABLED && gLogTrace) which preserves the constant check in the if statement.

However, this may be premature optimization. Regarding tracing, we already decided once before to trade potential compile-time optimization in favor of moving checks to runtime. I think it is acceptable to take another step in that direction unless we can produce meaningful benchmarks (or receive user feedback) suggesting otherwise.

Would like to hear others' thoughts before submitting approval.

[Julia-Garland]

As an additional note, I used the function call because gLogTrace is currently not included in mongoc-log-private.h