NFC Separate Emscripten and WASI standard lib disables in configure

[hoodmane]

In configure.ac in the "Modules that are not available on some platforms" we PY_STDLIB_MOD_SET_NA a bunch of standard library modules that either won't compile or won't work in Emscripten and WASI. Currently these two targets are overlapped, so there's a top level check for Emscripten|WASI and then a subcheck to decide which of the two cases we are dealing with. This entanglement minorly complicates maintenance of these targets. They should be disentangled.

This is a nonfunctional change.

Linked PRs

• gh-126178: NFC Separate Emscripten and WASI standard lib disables in configure #126179