fix(moore): select MCCL bfloat16 architecture

[voltjia]

Summary

Moore MCCL exposes mcclBfloat16 only when MARCH_TYPE describes a capable target architecture. InfiniCCL previously passed neither MARCH_TYPE nor an offload architecture to mcc, so BF16 collectives returned infinicclNotSupported even on S5000 hardware where MCCL supports them.

This PR adds an explicit and auto-detected MUSA architecture configuration, passes the matching compiler flags, and keeps mixed-architecture builds fail-closed.

Changes

• Architecture selection
  • Add MUSA_ARCHITECTURES, accepting forms such as 31, mp_31, and 3.1.
  • Prefer the explicit cache value, then TORCH_MUSA_ARCH_LIST, then native detection through musaGetDeviceProperties.
  • Fail with an actionable message when native detection is unavailable, such as during cross-compilation.
• MCCL capability mapping
  • Pass one --offload-arch=mp_* flag per configured target.
  • Define MARCH_TYPE from the least capable target because mccl.h exposes one global data-type table; this prevents a mixed fat binary from advertising BF16 on an unsupported target.
  • Apply the same architecture contract to the shared library and every Moore example target.
• Tests
  • Add CMake-script coverage for normalization, multiple compiler flags, fail-closed MARCH_TYPE, and invalid input.

Platform and Backend Affected

Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU

Backend

• OpenMPI
• MPICH
• NCCL
• MCCL

Performance Impact

• No performance impact
• Performance improved
• Performance regression possible

N/A. This changes build-time target selection and enables an existing MCCL data type.

Known Issues & Future Work

• Native architecture detection requires a visible MUSA device. Cross-builds must set MUSA_ARCHITECTURES or TORCH_MUSA_ARCH_LIST explicitly.

Test Results

Test Involved Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU

Test Involved Backend

• OpenMPI
• MPICH
• NCCL
• MCCL

Validated on Moore Threads S5000 with MUSA 4.3.6:

Explicit fat target 31;22:
  MUSA_ARCHITECTURES=31;22
  MARCH_TYPE=220
  compile flags: --offload-arch=mp_31 --offload-arch=mp_22 -DMARCH_TYPE=220
  InfiniCCL build: PASS
  CTest: 2/2 passed

Native detection:
  MUSA_ARCHITECTURES=31
  MARCH_TYPE=310
  compile flags: --offload-arch=mp_31 -DMARCH_TYPE=310
  InfiniCCL build: PASS
  BUILD_EXAMPLES=ON full build: PASS
  example compile flags: --offload-arch=mp_31 -DMARCH_TYPE=310
  CTest: 2/2 passed

Two-device BF16 AllReduce:
  input ranks: 1.0, 2.0
  output on both ranks: 3.0
  result: PASS

This commit was also combined with the open AllGather/Send/Recv stack at e8ccc0cb for InfiniLM validation. Qwen3-32B TP4 and Baichuan2-7B TP2 paged FlashAttention graph inference both passed after BF16 AllReduce became available.

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Checklist

Title, Branch, and Commits

• PR title follows Conventional Commits.
• Branch name follows the repository convention.
• Each commit message follows Conventional Commits.
• This is a single squashable commit.
• The branch is based cleanly on current master with no merge commit.
• No fixup, squash, or work-in-progress commits remain.

Scope and Design

• Changes are minimal and Moore-specific.
• No dead code, debug output, or unowned TODO remains.
• No unrelated formatting churn was introduced.
• The new build option is documented in its CMake cache description and errors.

General Code Hygiene

• Comments are limited to the non-obvious fail-closed fat-binary rule.
• Every modified or added file ends with one newline.
• git diff --check passes.
• Comments and error messages are English, complete sentences.

C++ Specific

N/A. No repository C++ source file is modified; the native detector is generated by CMake during configuration.

Python Specific

N/A. No Python file is modified.

Testing

• The Moore/MCCL library, CMake tests, and a two-device BF16 AllReduce were built and run successfully.

Build, CI, and Tooling

• Existing Moore and MCCL detection remains unchanged; architecture detection runs only when WITH_MOORE=ON.
• The branch is ready for repository CI.

Documentation

• The user-visible cache option and cross-build requirement are documented inline.
• No breaking change is introduced.

Security and Safety

• No secret, internal URL, customer data, or personal hardware identifier is committed.
• No third-party source code is added.
• No pointer arithmetic, memory access, or bounds-sensitive runtime code is changed.