databases/mongodb70: disable LTO for now

This was the error:
Checking if linker supports -flto... yes
lto compilation currently only works with the --linker=gold
See /wrkdirs/usr/ports/databases/mongodb70/work/mongo-r7.0.2/build/scons/config.log for details

• Error code 1

See logs for the full error:
https://pkg-status.freebsd.org/beefy18/data/main-amd64-default/pecb3f8a4918b_s8818f0f112/logs/mongodb70-7.0.2.log