Add rust-std-thumbv7em-none-eabihf output to rust feedstock - #2207

`auto-activate-base` is deprecated. Please use `auto-activate`. If your installer does not use the `base` environment as the default environment, also add `activate-environment: base`.

'nodefaults' channel detected: will remove 'defaults' if added implicitly. In the future, 'nodefaults' to remove 'defaults' won't be supported. Please set 'conda-remove-defaults' = 'true' in setup-miniconda to remove this warning.