Export the missing llhttp APIs via llhttp-ffi bindings (and ensure they're always updated)

[rdw-software]

Goals:

• [ ] The CI should fail if some function exported by the llhttp library wasn't bound

Quick prototype that I whipped up (Unix only): https://gist.github.com/Duckwhale/a66063ff1bd2d45fbdf4d3de9809065e

export-symbols.sh:

LLHTTP_LIB="libllhttp.so"

echo "Exporting symbols from $LLHTTP_LIB ..."
readelf -Ws $LLHTTP_LIB | awk '{print $8}' | grep llhttp_[^_] > llhttp_symbols.txt

Something like that could export the list of symbols and then a separate step in the OSX/Unix workflow can just run this test. Like the SIGPIPE one it could simply be skipped on Windows, although the tools might also be available in MSYS2?

The most important thing is that this can serve as a reminder, since manually checking for updated APIs is way too troublesome.