shell/new_call: Fix output streams contents being hidden from the user on error

subprocess.check_call, for some reason, does not log appropriately the contents of stdout on error, nor it crashes out when a shell is required.

This is the cause of a hidden failure when issuing ld to prelink all objects on macOS (!1341 (merged)), because I specified a glob that would be expanded by the shell, and this step never occurs because it's already passed verbatim to sh.