[RFC] Add GCC 10 and Clang 14 toolchain support (parallel branch)

[zarinn3pal]

Add GCC 10 and Clang 14 Toolchain Support

Fixes #200

Summary

This PR upgrades the cross-compilation toolchains across all supported MRI platforms to meet modern C++ standard requirements and resolve compatibility issues with contemporary libraries like Abseil.

Toolchain Upgrades:

• GNU Linux targets (x86_64, aarch64, arm, x86): GCC 9.x → GCC 10.5.0
• Musl Linux targets (all architectures): Unpinned GCC → GCC 10.3.0 (explicit version)
• Darwin/macOS targets (x86_64-darwin, arm64-darwin): Clang 10 → Clang 14.0.6

Problem Statement

Issue #200 identified that Abseil 20260526.0 requires GCC 10 or higher per Google's Foundational C++ Support Policy. Current rake-compiler-dock images are based on Ubuntu 20.04 with GCC 9.x toolchains, causing cross-compilation failures.

Changes

1. GNU Linux Targets (Dockerfile.mri.erb)

• Install explicit versioned packages: gcc-10-*, g++-10-*.
• Configure update-alternatives to set GCC 10 as system default.

2. Musl Linux Targets (build/mk_musl_cross.sh)

• Critical fix: Pin GCC_VER = 10.3.0 in config.mak.
• Pin BINUTILS_VER = 2.33.1 (newest version compatible with GCC 10).
• Eliminates non-deterministic builds from unpinned upstream dependencies.

3. Darwin/macOS Targets (Dockerfile.mri.erb + build/mk_osxcross.sh)

• Install Clang 14 from official LLVM APT repository.
• Update all llvm-10 references to llvm-14.
• Configure update-alternatives for clang/clang++ commands.
• Update osxcross build to use LLVM 14 toolchain.

4. Cross-Architecture Build Support (Dockerfile.mri.erb)

• Use existing TARGETPLATFORM to detect buildx host architecture.
• Install native vs. cross-compiler packages based on host for aarch64-linux-gnu and x86_64-linux-gnu targets(Also fixes ci failures).

Given the significant toolchain changes, I recommend treating this as a parallel branch rather than merging directly to main . To resolve the issue at its core, the base ubuntu version upgrade will be a better solution.

[yuanweiz]

I wonder if this can be a part of update-alternatives, but it might be out of scope of this PR. feel free to leave it as is.