litnmus-presi: adapt to ARM, this may be worthless,
due to the absence of timebase and of a cache flush instruction.
herd: Show cyclic relation when check fails in the the interpreter.
It proves convenient to extract sub-test from a rejectect execution.
NB: active with -debug barrier -v -gv
herd: make -debug model a synonym of -debug barrier
Merge branch 'master' of github.com:herd/herdtools