Fix --build_wasm_static_lib implicitly enable --build_wasm (#27342)
### Description
Moves the `--build_wasm_static_lib → --build_wasm` implication from
`build.py` into `build_args.py`'s post-processing, **before** the cmake
generator selection. Previously, `build_args.py` chose the generator
based on `args.build_wasm` (still `False`), and `build.py` only set it
to `True` afterwards—too late.
- **`tools/ci_build/build_args.py`**: Set `args.build_wasm = True` when
`args.build_wasm_static_lib` is set, prior to generator and
cross-compilation logic.
- **`tools/ci_build/build.py`**: Remove the now-redundant identical
check.
### Motivation and Context
Using `--build_wasm_static_lib` without `--build_wasm` caused cmake to
use the wrong generator (e.g., Visual Studio instead of Ninja on
Windows) and miss Emscripten-specific configuration, leading to build
failures like missing `libiconv`.
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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: fs-eire <7679871+fs-eire@users.noreply.github.com>