Work around excessive command-line length issues by
disabling incremental rust compilation, which is enabled
by default outside `cargo --release` starting with Rust 1.24.
Incremental rust builds shouldn't help much in automation,
where sccache provides the only continuity between build
environments. In the meantime, they add a lot of object
files to the link line.
See https://github.com/rust-lang/rust/pull/47507 about addressing
the underlying issue upstream.
MozReview-Commit-ID: LRwUj3fhiaO
--HG--
extra : rebase_source : 1739a7570b2e7fe40ead3b301ea20c2fe79f0431
