rust: Upgrade 1.89.0 -> 1.90.0

rust: Upgrade 1.89.0 -> 1.90.0

https://blog.rust-lang.org/2025/09/18/Rust-1.90.0/

* Recent changes in rustc require 'target-c-int-width' to be an integer,
  not a string. This fixes type consistency when generating target specs.
  https://github.com/rust-lang/rust/pull/142352.

* Rebase existing patches with v1.90.0.

* Drop merged patches with rust v1.90.0.
  - backport-fix-test-string-merging.patch
  https://github.com/rust-lang/rust/commit/2d51acd2fbcbadb6f30709c5dd305494d413d388

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

  The tests/{assembly/codegen} dirs are renamed to
  tests/{assembly,codegen}-llvm. Update the test suite and
  patches accordingly.
  https://github.com/rust-lang/rust/pull/144249/commits

* Use "//@ ignore-riscv64" tag for tests failing on riscv-64 instead of previous
  "only-<target_arch>" tags.

  Test results summary:

   rust v1.90.0
   +-----------+--------+---------+
   | Machine   | Passed | Ignored |
   +-----------+--------+---------+
   | arm-32    | 29,517 |  1,529  |
   | arm-64    | 29,608 |  1,471  |
   | x86-32    | 29,508 |  1,507  |
   | x86-64    | 29,903 |  1,275  |
   | riscv-64  | 29,584 |  1,494  |
   +-----------+--------+---------+

   Test results difference (1.90 - 1.89):
   +-----------+--------+---------+
   | Machine   | Passed | Ignored |
   +-----------+--------+---------+
   | arm-32    |  +278  |   +61   |
   | arm-64    |  +279  |   +59   |
   | x86-32    |  +277  |   +58   |
   | x86-64    |  +419  |   +50   |
   | riscv-64  |  +280  |   +58   |
   +-----------+--------+---------+

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