Upgrade to Rust 1.96.0 and adapt BlueOS targets for the new toolchain

[wangchen-vivo]

Upgrade to Rust 1.96.0 and rebase BlueOS patches

Note: This PR is in draft until the BlueOS libc and cc-rs PRs are
merged. The libc / cc-rs git revision pinned in the lockfiles and
ALLOWED_SOURCES will be updated to the final merged commit SHAs before
marking this PR ready for review.

Background

BlueOS maintains a fork of rustc with patches that add the BlueOS target specs
and adapt std to the BlueOS libc / newlib runtime. The previous fork was
based on Rust 1.84.0 (blueos-dev branch).

This branch rebases those BlueOS patches onto the Rust 1.96.0 stable release
and resolves the conflicts caused by upstream changes between 1.84 and 1.96.

What this PR does

BlueOS target specs & std support

• Cherry-pick of [BlueOS] Support vivo BlueOS — the original commit that
  adds the six BlueOS target specs and wires up std for the BlueOS newlib
  runtime. Adapted to 1.96:

  • Migrate cfg_if! to cfg_select! in sys/ modules.
  • Move BlueOS cfg entries from pal/unix/os.rs to sys/paths/unix.rs.
  • Move BlueOS cfg entries from pal/unix/process/ to sys/process/unix/.
  • Add BlueOS to pal/unix/sync/condvar.rs cfg lists.
  • Add BlueOS to fs/unix.rs link() no-linkat fallback.

• Cherry-pick of Fix: bootstrap abi issue — adapt the BlueOS stat time
  accessors and process module to 1.96:

  • Move from scalar (st_atime / st_mtime / st_ctime) to timespec
    (st_atim / st_mtim / ctim) in sys/fs/unix.rs.
  • Add BlueOS to sys/process/unix/mod.rs allow(unused) cfg_attr.

Target spec adjustments

• PIC relocation model by default for riscv64-vivo-blueos (needed to
  build static PIE).
• emutls for riscv32imc-vivo-blueos — same workaround as rv32imac,
  the native TLS is not available on this target yet.
• Dynamic linking & PIC on Cortex-M — enable dynamic_linking and PIC
  for thumbv7m-vivo-blueos-newlibeabi and thumbv8m.main-vivo-blueos-newlibeabihf.

libc fork pin

• Pin the BlueOS libc fork to the commit that adapts it to Rust 1.96
  (2f8715c4) across Cargo.lock, library/Cargo.lock, and the tidy
  ALLOWED_SOURCES list (src/tools/tidy/src/extdeps.rs).
• Set c_char = i8 on BlueOS targets in library/core/src/ffi/primitives.rs
  (BlueOS compiles C with -fsigned-char).

Build / CI

• Remove potential GPL components — drop pr-check-1/ (Dockerfile,
  reuse-requirements, etc.) and its references in tidy/Dockerfile.
• Don't build clang in config.blueos.toml — clang is installed via the
  package manager, saving build time.
• Build sanitizers on Linux and Darwin in config.blueos.toml.
• Strip binaries to avoid exhausting the GitHub Actions runner's disk.
• macOS build fix in config.blueos.toml.
• Bump bootstrap and profiler_builtins Cargo metadata.

Testing

Verified by building the full BlueOS Rust toolchain via x.py install for
compiler/rustc and std across all BlueOS targets.

[CLAassistant]

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3 out of 4 committers have signed the CLA.

✅ lawkai-vivo
✅ wangchen-vivo
✅ zhanghe-vivo
❌ nooopslol
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