gh-129666: Add C11/C++11 to docs and -pedantic-errors to GCC/clang test_c[pp]ext...

gh-129666: Add C11/C++11 to docs and -pedantic-errors to GCC/clang test_c[pp]ext tests (GH-130692)

Disable pedantic check for c++03 (unlimited API)

Also add a check for c++03 *limited* API, which passes in pedantic mode
after removing a comma in the `PySendResult` declaration, and allowing
`long long`.