Port patch to bytes v1.6

[marius-meissner]

As this patch is still required, we should port it to v1.6.
Please create a separate branch and name it similarly, e.g. cfg_target_has_atomic_v1.6.0.

Furthermore, please adjust README in main branch to indicate these two branches.

[HusseinAbdelhamid]

Is there a way to make sure that the port is successful locally on this branch? because in either this or the v1.3.0 branch i get the same errors when i build for target thumbv6m with the default features disabled. My approach was basically to merge the current master branch of bytes crate into the branch cfg_target_has_atomic_v1.6.0 (which is a branch from v1.3.0)