Add .swift_ast to list of Swift sections (llvm#66426)

(cherry picked from commit e8ad9b0)

Author: adrian-prantl

llvm/include/llvm/BinaryFormat/Swift.def

@@ -31,3 +31,4 @@ HANDLE_SWIFT_SECTION(protocs, "__swift5_protos", "swift5_protocols",
 HANDLE_SWIFT_SECTION(acfuncs, "__swift5_acfuncs", "swift5_accessible_functions",
                      ".sw5acfn$B")
 HANDLE_SWIFT_SECTION(mpenum, "__swift5_mpenum", "swift5_mpenum", ".sw5mpen$B")
+HANDLE_SWIFT_SECTION(swiftast, "__swift_ast", "swift_ast", "swiftast");