feat(util/thread): add atomic_uchar
feat(util/thread): add atomic_uchar

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

soonhokong/travis_test,digama0/lean,fgdorais/lean,digama0/lean,johoelzl/lean,dselsam/lean,fpvandoorn/lean,avigad/lean,fpvandoorn/lean2,rlewis1988/lean,johoelzl/lean,levnach/lean,fpvandoorn/lean2,htzh/lean,leodemoura/lean,johoelzl/lean,leanprover-community/lean,johoelzl/lean,Kha/lean,dselsam/lean,Kha/lean,fpvandoorn/lean,c-cube/lean,soonhokong/lean-osx,leodemoura/lean,rlewis1988/lean,c-cube/lean,levnach/lean,javra/lean,dselsam/lean,leodemoura/lean,soonhokong/lean-osx,soonhokong/lean,eigengrau/lean,avigad/lean,rlewis1988/lean,htzh/lean,soonhokong/lean,leanprover/lean,Kha/lean,avigad/lean,leanprover/lean,dselsam/lean,rlewis1988/lean,c-cube/lean,soonhokong/lean-osx,javra/lean,fpvandoorn/lean,UlrikBuchholtz/lean,dselsam/lean,eigengrau/lean,UlrikBuchholtz/lean,javra/lean,leodemoura/lean,digama0/lean,digama0/lean,fgdorais/lean,fgdorais/lean,Kha/lean,eigengrau/lean,soonhokong/travis_test,soonhokong/lean,htzh/lean,johoelzl/lean,fgdorais/lean,javra/lean,levnach/lean,leodemoura/lean,c-cube/lean,levnach/lean,fpvandoorn/lean2,htzh/lean,sp3ctum/lean,leanprover-community/lean,avigad/lean,soonhokong/travis_test,soonhokong/lean-osx,c-cube/lean,soonhokong/lean-windows,fpvandoorn/lean2,sp3ctum/lean,avigad/lean,fgdorais/lean,leanprover/lean,fgdorais/lean,leodemoura/lean,fpvandoorn/lean2,soonhokong/lean,sp3ctum/lean,Kha/lean,levnach/lean,Kha/lean,htzh/lean,fpvandoorn/lean,digama0/lean,sp3ctum/lean,leanprover-community/lean,avigad/lean,soonhokong/lean,johoelzl/lean,digama0/lean,UlrikBuchholtz/lean,eigengrau/lean,leanprover-community/lean,UlrikBuchholtz/lean,soonhokong/lean-windows,UlrikBuchholtz/lean,fpvandoorn/lean,fpvandoorn/lean,dselsam/lean,leanprover/lean,sp3ctum/lean,soonhokong/lean-windows,eigengrau/lean,leanprover-community/lean,soonhokong/travis_test,soonhokong/lean-windows,rlewis1988/lean,rlewis1988/lean,leanprover/lean,soonhokong/lean-windows,javra/lean,leanprover/lean,soonhokong/lean-osx,leanprover-community/lean