[clang] [clang-tools-extra] [lldb] [clang] implement CWG1980 and CWG2064: instantiation-dependency improvements (PR #190495)

[Oliver Hunt via cfe-commits]

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@@ -7399,17 +7480,50 @@ TemplateName ASTContext::getCanonicalTemplateName(TemplateName Name,
       // Keep popping from the back any deault arguments which are the same.
       if (I == int(CanonArgs.size() - 1))
         CanonArgs.pop_back();
-      NonCanonical = true;
+      AnyChanged = true;
+    }
+    return AnyChanged ? getDeducedTemplateName(
----------------
ojhunt wrote:

I think this would be easier to read as 
```cpp
if (!AnyChanged)
  return Name;
return getDeducedTemplateName(.....);
```

https://github.com/llvm/llvm-project/pull/190495