[CI] re-enable wasm CPU tests (#24801)
### Description
<!-- Describe your changes. -->
1. re-enable wasm CPU tests. It was originally enabled but was later
disabled in a change that treat wasm build as cross-compiling.
2. Use build.py to populate the environment variables.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
