Commit c4f5dfad0d was intended as a stylistic cleanup, but the trailing \ it
removed from pkgs/build-support/rust/lib/default.nix was not stylistic: it is a
shell line continuation that joins the cross-only env var block to the cargo
command added by consumers. Without it, `CC_*`, `CXX_*`, and
`CARGO_TARGET_*_LINKER` are silently not passed to cargo when
rustTargetPlatform != rustHostPlatform.
This in turn can break cross compilation of Rust packages.
Fix it by adding back the trailing \
Fixes: #497857
Signed-off-by: Gilberto Bertin <me@jibi.io>
Gilberto Bertin
42955023b2