Historically, Rust's Fuchsia targets have been labeled x86_64-fuchsia
and aarch64-fuchsia. However, they should technically contain vendor
information. This CL changes Fuchsia's target triples to include the
"unknown" vendor since Clang now does normalization and handles all
triple spellings.
This was previously attempted in #90510, which was closed due to
inactivity.
f6ef039775