Make use of nested specialization patterns.

1 job for master in 6 minutes and 7 seconds (queued for 1 second)
Status Job ID Name Coverage
failed #21793


Name Stage Failure
failed Build
Makefile.coq:317: recipe for target 'all' failed
make[1]: *** [all] Error 2
Makefile:6: recipe for target 'all' failed
make: *** [all] Error 2

real 5m4.725s
user 23m19.260s
sys 0m33.556s
ERROR: Job failed: exit code 1