Allow to define `COMMIT` by env
Allow to define `COMMIT` by env

Some package managers download the archive instead of cloning the git repo.
When they do that, the call to git fails.

This commit allows package managers to provide the COMMIT value via environment.

Signed-off-by: Julien Durillon <3566766e6f85b3995d0cbd3247dbc901ed9b65ae@clever-cloud.com>

opencontainers/runc,rhatdan/runc,opencontainers/runc,dqminh/runc,xiaochenshen/runc,opencontainers/runc,mikebrow/runc,rhatdan/runc,justincormack/runc,estesp/runc,opencontainers/runc,mheon/runc,rhatdan/runc,adrianreber/runc,mheon/runc,dqminh/runc,xiaochenshen/runc,kolyshkin/runc,mheon/runc,estesp/runc,adrianreber/runc,justincormack/runc,mYmNeo/runc,mikebrow/runc,xiaochenshen/runc,kolyshkin/runc,kolyshkin/runc,mikebrow/runc,justincormack/runc,dqminh/runc,estesp/runc,mYmNeo/runc,adrianreber/runc,rhatdan/runc,kolyshkin/runc,dqminh/runc,mYmNeo/runc