[clang-tools-extra] [clang-tidy] Fix invalid fix-it for macro expansions (PR #227984)

[Zeyi Xu via cfe-commits]

================
@@ -101,11 +101,14 @@ void PreferSingleCharOverloadsCheck::check(
   if (!Replacement)
     return;
 
-  diag(Literal->getBeginLoc(), "%0 called with a string literal consisting of "
-                               "a single character; consider using the more "
-                               "efficient overload accepting a character")
-      << FindFunc
-      << FixItHint::CreateReplacement(Literal->getSourceRange(), *Replacement);
+  const auto Diag = diag(Literal->getBeginLoc(),
+                         "%0 called with a string literal consisting of "
+                         "a single character; consider using the more "
+                         "efficient overload accepting a character")
+                    << FindFunc;
+  if (!Literal->getBeginLoc().isMacroID() && !Literal->getEndLoc().isMacroID())
----------------
zeyi2 wrote:

Could we check all concatenated string tokens rather than only the endpoints?

```c
#define SEP "_"
...
s += "" SEP "";
```

I think we also want to stop emitting fix-its for similar cases like this.

```c++
if (std::none_of(Literal->tokloc_begin(), Literal->tokloc_end(),
                 [](SourceLocation Loc) { return Loc.isMacroID(); }))
```

https://github.com/llvm/llvm-project/pull/227984