Python wheels on Linux require statically linked SSL libraries.
We were previously relying on the native-tls-vendored feature in
reqwest, but that does not work with Bazel, as openssl-src makes
assumptions that break when sandboxed. The static libs distributed
by distros like Ubuntu fail to link, and while we could potentially
build OpenSSL ourselves, we'd then need to keep it up to
date.
On Windows and Mac however, native-tls is preferable to ring, as it
allows us to get free updates from the OS, and results in
a smaller library.
Rust currently only supports platform-specific features in nightly,
and cargo-raze does not have support for them, so we currently need
to override the generated build file with a hand-crafted one that
specifies the relative features/deps for each platform.
update.py has been updated to automatically keep the version numbers
in this file up to date, so it should hopefully not prove too hard to
maintain going forward.
