feat(library/module): do not use threads when lean is not compiled with LEAN_MULTI_THREAD
feat(library/module): do not use threads when lean is not compiled with LEAN_MULTI_THREAD

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

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