Ben Gamari authored May 05, 2021 and Moritz Angermann committed May 06, 2021

Previously Hadrian depended implicitly upon whatever `bash` it found in
`PATH`, offerring no way for the user to override. Fix this by detecting
`sh` in `configure` and passing the result to Hadrian.

Fixes #19797.

(cherry picked from commit bf34a310)