[ck0i]

Fixes #3474
Fixes #3464

Root cause

libclang has no CXType_Char8, so a char8_t type reaches build_builtin_ty as CXType_Unexposed and gets no builtin mapping. Scalar uses still came out as u8 through the fallback path, but an array element type returned ParseError::Recurse and the CXType_ConstantArray arm panicked with Not able to resolve array element?. Enum::from_ty also could not resolve the underlying type and treated it as signed, so enum class E : char8_t { HEX = u8'\xFF' } produced pub type E = i8 and E_HEX = -1.

Fix

• In build_builtin_ty, map an unexposed type whose canonical spelling is char8_t (ignoring const/volatile) to IntKind::U8.
• Add a char8_t.hpp test covering fixed, incomplete and nested arrays, a struct field array, a function parameter and an enum with a char8_t underlying type.
• Add a CHANGELOG entry.

Testing

Ubuntu (WSL), libclang 21.1.8, rustc 1.99.1.

• Before: cargo test -p bindgen-tests -- char8_t aborts with Not able to resolve array element?: Recurse.
• After: the new test passes. The arrays come out as [u8; N] and the enum as pub type Char8Enum = u8 with Char8Enum_High = 255.
• cargo test -p bindgen-tests -p bindgen leaves every other expectation file unchanged, and cargo +nightly fmt -- --check is clean.