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>

Author: Copilot

tools/ci_build/build.py

@@ -2327,9 +2327,6 @@ def main():
         if args.nnapi_min_api < 27:
             raise BuildError("--nnapi_min_api should be 27+")
 
-    if args.build_wasm_static_lib:
-        args.build_wasm = True
-
     if args.build_wasm:
         if not args.disable_wasm_exception_catching and args.disable_exceptions:
             # When '--disable_exceptions' is set, we set '--disable_wasm_exception_catching' as well

tools/ci_build/build_args.py

@@ -938,6 +938,10 @@ def convert_arg_line_to_args(self, arg_line: str) -> list[str]:  # Use list[str]
     if args.android_ndk_path:
         args.android_ndk_path = os.path.normpath(args.android_ndk_path)
 
+    # Treat --build_wasm_static_lib as implying --build_wasm
+    if args.build_wasm_static_lib:
+        args.build_wasm = True
+
     # Handle WASM exception logic
     if args.enable_wasm_api_exception_catching:
         args.disable_wasm_exception_catching = True  # Catching at API level implies disabling broader catching