wasm-sourcemap.py invocation change drops PYTHONPATH, breaks Bazel builds

[stephenduong1004]

The recent sourcemap improvements in commit #23741 introduced a change in how wasm-sourcemap.py is invoked, now using python exec-ing python. This causes environment variables like PYTHONPATH to be dropped.

This creates issues when building in isolated environments like Bazel, where third-party dependencies are not in the standard paths and rely on PYTHONPATH.

[sbc100]

I don't see anything in #23741 that changes the way wasm-sourcemap.py is run.

It looks like we have been doing PYTHON, "-E", path_from_root('tools/wasm-sourcemap.py' since at least back in #16736

[sbc100]

I uploaded #25373 which should fix the issue.

Although I still don't know what change broke you here since AFAICT we have always run wasm-sourcemap.py with -E (ignoring PYTHONPATH).