I prefer to emit the messages, just make them more user-friendly
("searching for program" "no such file or directory" is not very
friendly, IMO), and suppress the error signaling even when
debug-on-error is non-nil. The reason is simple: we are talking only
about Git not being installed or accessible here, but the problems
could be different and more obscure: Git could be present but
inoperable for some weird misconfiguration reason, or some other
problem could happen. So "if it is not installed, just silently don't
do anything" is not a complete solution, and the "silently" part loses
information which users may wish to have presented to them.