Adapts call side to the API change in LLVM20 of
`unsigned int clang::FieldDecl::getBitWidthValue() const`
--- a/c2rust-ast-exporter/src/AstExporter.cpp	2025-02-24 14:19:52.000000000 +0100
+++ b/c2rust-ast-exporter/src/AstExporter.cpp	2025-03-14 09:39:10.440335997 +0100
@@ -2209,7 +2209,14 @@ class TranslateASTVisitor final
                          // 2. Encode bitfield width if any
                          if (D->isBitField()) {
                              cbor_encode_uint(
-                                 array, D->getBitWidthValue(*this->Context));
+                                 array,
+
+#if CLANG_VERSION_MAJOR >= 20
+                                D->getBitWidthValue()
+#else
+                                D->getBitWidthValue(*this->Context)
+#endif
+                            );
                          } else {
                              cbor_encode_null(array);
                          };