Improve cross-platform ASM toolchain discovery and Apple Silicon / arm64 support

[JackTriton]

Improve cross-platform ASM toolchain discovery and Apple Silicon support

This PR updates the ASM build script to support the Apple Silicon n64 toolchain without changing the existing Windows, Linux, or Intel macOS workflows.

Before this, both of these need to be merged:

• Add Apple Silicon support and optional local toolchain sources glankk/n64#32
• Add Apple Silicon / arm64-compatible n64 formula and optional local sources homebrew-tap#5

Changes

• Add common MIPS toolchain discovery for:

  • project-local tools
  • OOTR_N64_PREFIX
  • standard Homebrew n64 prefixes
  • the system PATH

• Place generated toolchain wrappers under the shared ASM/tools/toolchain directory.

• Ensure GCC, assembler, linker, objdump, and objcopy are selected from the same toolchain prefix.

• Add an isolated assembler launch environment on Apple Silicon to avoid interference from Conda, MacPorts, or inherited compiler variables.

• Clear COMPILER_PATH and GCC_EXEC_PREFIX before invoking the toolchain.

• Add optional mips64-g++ support.

• Add:

python3 build.py --check-toolchains

This command reports the expected path, detected path, resolved path, version, ROM size, and GCC-selected assembler for every required file and executable.

• Preserve existing build behavior on other platforms.
• Support both the existing fixed payload layout and branches that use a configurable payload start, depending on the selected patch version.

Compatibility

The Apple Silicon-specific behavior is enabled only when running on Darwin arm64. Other platforms continue to use the existing direct tool execution path.

[flagrama]

This just looks like slop to me. It doesn't even look like it even checks the PATH for a valid toolchain which is the default way to do it. The tools directory is there for people who don't know how to modify their PATH. I'm against even reviewing this because there is a clear lack of actual understanding of what is actually being done for randomizer and why.

[flagrama]

The only review I'll do is that the README file is so wordy as to be completely useless and ignored now. The readme should be the recommended path for each platform. Do not add a bunch of "do this or this" and "you can do this but it is optional". Create a new file for advanced concepts.