only one let binding

TODO: This branch is probably not a good idea since it recreates a lot
of let-bindings instead of sharing them.
1 job for time/one-let-bind in 8 minutes and 58 seconds (queued for 8 seconds)
Name Stage Failure
build-coq.8.14.0-timing Build
of Qed.

make: *** [Makefile:6: all_with_examples] Error 1

real 7m35.398s
user 38m26.430s
sys 5m14.056s
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1