build: ensure toolchain is passed to bundled deps #37587

Problem:
When building Neovim with Emscripten for WebAssembly, the
`CMAKE_TOOLCHAIN_FILE` is not propagated to dependency builds.
So libuv attempts to include Linux-specific headers like
`sys/epoll.h` which don't exist in the WebAssembly environment.

From #37572:

    …/NeovimWeb/external/neovim/.deps/build/src/libuv/src/unix/linux.c:44:10:
    fatal error: 'sys/epoll.h' file not found
       44 | #include <sys/epoll.h> |          ^~~~~~~~~~~~~

Solution:
1. Add initialization for DEPS_CMAKE_ARGS to prevent CMake errors.
2. Implement conditional logic to always pass CMAKE_TOOLCHAIN_FILE to
   dependencies.

This allows dependencies like libuv to detect they're building for
WebAssembly and disable incompatible Linux specific features such as
epoll which resolves the sys/epoll.h error.

0 files changed, 0 insertions, 0 deletions