[libclang] Handle AutoType in clang_getTypeDeclaration

[skalinichev]

Summary

Now that auto type is fixed by D11976, it also makes sense to support it in clang_getTypeDeclaration.

[milianw]

Adding tests wouldn't hurt though, quite the contrary. Especially if it wasn't tested before. Otherwise, this looks good to me.

[klimek]

+1 to "not tested before" not implying "doesn't need tests" :)

[skalinichev]

Added tests

[milianw]

lgtm, but someone else should approve

[klimek]

lg

tools/libclang/CXType.cpp

       D = cast<TemplateSpecializationType>(TP)->getTemplateName()
                                                          .getAsTemplateDecl();
     break;
-      
+  case Type::Auto:
+    TP = cast<AutoType>(TP)->getDeducedType().getTypePtrOrNull();
+    if (TP)
+      goto try_again;
+    break;
+
   case Type::InjectedClassName:
     D = cast<InjectedClassNameType>(TP)->getDecl();
     break;