Add --noarch-build-subdir option

[mingwandroid]

It would be nice to know that we can still build noarch and noarch python on other
OSes (well, except Windows at present). This allows that.

Also, in combination with --output-dir it allows building locally as would happen on
c3i. A sample script to glue this together is:

#!/usr/bin/env bash

set -e
FS_STUB=$1

__conda_setup="$(/opt/conda/bin/conda 'shell.bash' 'hook' 2> /dev/null)"
if [ $? -eq 0 ]; then
    eval "$__conda_setup"
fi

if [[ $(uname) == Darwin ]]; then
  BUILD_SUBDIR=osx-64
elif [[ $(uname) =~ M.* ]]; then
  BUILD_SUBDIR=win-64
else
  BUILD_SUBDIR=linux-64
fi

mkdir /tmp/$$.c3i-locally
pushd /tmp/$$.c3i-locally
  conda activate
  cp -rf /opt/r/a/$FS_STUB-feedstock .
  cp -f /opt/r/a/conda_build_config.yaml .
  c3i one-off rdonnelly.$FS_STUB  \
              $FS_STUB-feedstock  \
              --config-root-dir=/opt/asrc/automated-build/c3i_configurations/github_public  \
              --dry-run  \
              --output-dir $PWD  \
              --noarch-build-subdir ${BUILD_SUBDIR}  \
              --no-skip-existing
  mkdir rsync-recipes
  cp -rf *-on-* rsync-recipes/
  mkdir stats
  cmds=$(cat plan.yml | yq -r '.jobs[0].plan[] | select(.task=="build").config.run.args[1]')
  echo $cmds
  conda deactivate
  eval ${cmds}
popd