Add support for serial tail calls.

Currently once we are serial no more parallel strains are executed. However, this could be changed using strain local resources in the future.
3 jobs from master in 4 minutes 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #3836
build_cmake

01:00

 
  Test
passed #3837
run_tests

01:00

 
  Sanitizer
passed #3838
run_address_sanitizer

02:00