[toolchain] Improve rust WASM toolchain script arg validation (#35684)

This adds extra checks for some of the arguments in this script to make
srue they are not coming across empty in CI.

Bug: https://github.com/brave/brave-browser/issues/54478

tools/rust/build_rust_toolchain_standalone.py

@@ -397,6 +397,7 @@ class ToolchainBuilder:
                               target_triple / STAGE1_RUSTLIB)
         output_archive = self.out_dir / self._package_name()
 
+        logging.info('Creating output archive at %s', output_archive)
         with tarfile.open(output_archive, 'w:xz') as tar:
             tar.add(Path(self.build_rust_module.RUST_HOST_LLVM_INSTALL_DIR) /
                     'bin' / LLD,
@@ -582,6 +583,11 @@ def main():
                         help='Enable verbose (debug) logging')
     args = parser.parse_args()
 
+    if not args.chromium_src:
+        parser.error('--chromium-src cannot be empty')
+    if not args.out_dir:
+        parser.error('--out-dir cannot be empty')
+
     if args.clone_chromium and not args.use_ref:
         parser.error('--use-ref is required when --clone-chromium is provided')