databases/mongodb60: reduce warning output

The build outputs MBs of reports like:
"warning: builtin has_trivial_assign is deprecated; use is_trivially_assignable instead [-Wdeprecated-builtins]"

This might somehow supress the error output (or cause the error) of the sporadic "Error -9".

Suggested by: des@ via https://lists.freebsd.org/archives/freebsd-ports/2025-May/007910.html