## Why
Windows builds combine Cygwin build tools with native MSVC outputs. On ARM64,
Cygwin can run under x64 emulation, so inferred host details and untranslated
paths can select the wrong target or leak POSIX paths into native metadata.
## What changed
- Convert libffi source, prefix, and shell paths with `cygpath`, preserve
`USERPROFILE`, and pass explicit build and host targets.
- Configure libffi's MSVC and libtool environment to produce and install its
shared library and import library, including across recursive make calls.
- Reject libffi pkg-config output containing `/cygdrive/` paths and enable
Opus NEON support for `aarch64-pc-windows-msvc`.
- Document the additional Windows build prerequisites.
## Testing
- Extend `test_build_native.py` with Windows path conversion, x64 and ARM64
target configuration, recursive make flag propagation, pkg-config, and Opus
coverage.
GitOrigin-RevId: 12eb4ff83e141aa069abd68af4839f06e4c45b8f
## Why
The pinned voice source inputs can be prepared but do not yet provide compiled
native libraries for downstream integration.
## What changed
- Add `build_native.py` to build a shared-library prefix for the supported voice
dependencies on native x64 and ARM64 GNU/Linux, macOS, and Windows MSVC hosts.
- Require explicit toolchain inputs, isolate dependency discovery to the output
prefix, and record command logs and build state for provenance and failures.
- Expose the recipe and source inputs through `//third_party/voice:build_inputs`
and document its prerequisites, outputs, and integration boundaries.
## Testing
- `PYTHONSAFEPATH=1 python3 -m unittest discover -s third_party/voice -p 'test_build_native.py'`
GitOrigin-RevId: 132d93561a8e1bb178518f1248cf87d031060aae
Benjamin Carlsson