rust: Upgrade 1.90.0 -> 1.91.0

rust: Upgrade 1.90.0 -> 1.91.0

https://blog.rust-lang.org/2025/10/30/Rust-1.91.0/

* Recent updates to rustc now require 'target_pointer_width'
  to be specified as an integer.
  Cast it to 'int' in rust target configuration to resolve the
  type consistency error.
  https://github.com/rust-lang/rust/pull/144443

* The "remote-test-server" bin is now generated in stage2-tools-bin dir
  rather than stage1. Update the test suite and recipe accordingly.

* Rebase existing patches with v1.91.0.

* Drop merged patches with rust v1.91.0.
  - 0001-libunwind-Use-gcs-instead-of-gcs-target-attribute.patch
    https://github.com/llvm/llvm-project/pull/138077/commits/bcc31a9384d2df1c0f27ef140e1f0f9ee493034f

Signed-off-by: Yash Shinde <Yash.Shinde@windriver.com>
Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>