[build] Fix the issue about python3 not found

Change-Id: Ie1e26c4d5f2beac39d3078336daf7eef8df1f271
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/yasm/+/948173
Reviewed-by: Petr Hosek <phosek@google.com>
diff --git a/yasm_assemble.gni b/yasm_assemble.gni
index f0f98d2..e292297 100644
--- a/yasm_assemble.gni
+++ b/yasm_assemble.gni
@@ -106,6 +106,8 @@
     yasm_path = get_label_info(yasm_label, "root_out_dir") + "/yasm"
     args = [
       clang_prefix,
+      rebase_path(python_exe_src, root_build_dir),
+      "-S",
       rebase_path(run_yasm_script, root_build_dir),
     ]