Set output file for FPRINT benchmark.

The FPRINT benchmark needs a file and it was set to "/tmp/fprint.tst",
which doesn't exist on gitlab CI.  Just use "./tmp/fprint.tst".

Let CI recipes create the "tmp" directory so the scripts don't need
to.
2 jobs for rtoy-issue-87-add-cl-bench in 11 minutes and 8 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed linux-runner #4264
linux

00:08:25

passed osx-runner #4265
osx

00:11:08