cmd/buildlet: fix bash wrapper check for iOS
cmd/buildlet: fix bash wrapper check for iOS

Updates golang/go#41610

Change-Id: I9a2e151eaf8104e2f3a1a8d36f8dc72a6351fd4a
Reviewed-on: https://go-review.googlesource.com/c/build/+/259580
Trust: Elias Naur <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@eliasnaur.com>
Run-TryBot: Elias Naur <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@eliasnaur.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/build,golang/build,golang/build,golang/build