[clang] [clang][FMV] Do not omit explicit default target_version attribute. (PR #96628)

[Alexandros Lamprineas via cfe-commits]

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@@ -11576,22 +11584,6 @@ static bool CheckTargetCausesMultiVersioning(Sema &S, FunctionDecl *OldFD,
     }
   }
 
-  if (NewTVA) {
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labrinea wrote:

This is checking things like
```
//expected-note at +1 {{previous declaration is here}}
void __attribute__((target_version("bti+flagm2"))) one(void) {}
//expected-error at +1 {{multiversioned function redeclarations require identical target attributes}}
void __attribute__((target_version("flagm2+bti"))) one(void) {}
 ```
 (example taken from clang/test/Sema/attr-target-version.c)
 
 At this point we know that the new declaration is triggering multiversioning therefore the old was the (implicit or explicit) default.

https://github.com/llvm/llvm-project/pull/96628