Minor adjustment to coordinating thread spawns (catch seems to have problems…

Minor adjustment to coordinating thread spawns (catch seems to have problems with the other implementation).
3 jobs from master in 4 minutes 37 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #3951
build_cmake

01:07

 
  Test
passed #3952
run_tests

01:07

 
  Sanitizer
passed #3953
run_address_sanitizer

02:23