CI: rfl: upgrade to v6.17-rc3 plus 2 temporary commits

This upgrades the Rust CI from v6.16-rc1 plus a temporary commit for
the >= 1.91 target spec [1] to v6.17-rc3 with two temporary commits --
one for the same target spec format change [1] and another for the
`file_as_c_str` change [2].

Link: rust-lang#144443 [1]
Link: rust-lang#145928 [2]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

src/ci/docker/scripts/rfl-build.sh

@@ -3,7 +3,7 @@
 set -euo pipefail
 
 # https://github.com/rust-lang/rust/pull/144443
-LINUX_VERSION=7770d51bce622b13195b2d3c85407282fc9c27e5
+LINUX_VERSION=8851e27d2cb947ea8bbbe8e812068f7bf5cbd00b
 
 # Build rustc, rustdoc, cargo, clippy-driver and rustfmt
 ../x.py build --stage 2 library rustdoc clippy rustfmt