WASM build scripts don't honour `--with-pydebug` from build-python due to a `sysconfig` regression

[FFY00]

Bug report

Bug description:

2950bc5 inadvertently caused -pydebug to no longer be appended to pybuilddir.txt.

Since the WASM build scripts look for it on the build-python's pybuilddir.txt to decide whether or not to configure the host with --with-pydebug, they stopped honoring the build-python configuration.

I noticed this when I unintentionally fixed it in GH-131761, which uncovered another issue, GH-130397.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

No response

Linked PRs

• [3.14] GH-131769: fix detecting a pydebug build of the build Python when building for WASI #133219
• GH-131769: fix detecting a pydebug build of the build Python when building for WASI #134015

[brettcannon]

I think it's fine to call the build Python and just have it exit with 1 or 0 based on whether it's a debug build to avoid any future regressions: python -c "import sys; sys.exit(hasattr(sys, 'gettotalrefcount'))".

[brettcannon]

I have a PR up at #133219 which fixes the issue in a permanent way. I have it labeled as DO-NOT-MERGE until #131770 is fixed.