[clang] [Clang][Sema] Accept weak reference after declaration (PR #228809)

[via cfe-commits]

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@@ -8804,6 +8804,31 @@ NamedDecl *Sema::DeclClonePragmaWeak(NamedDecl *ND, const IdentifierInfo *II,
 void Sema::DeclApplyPragmaWeak(Scope *S, NamedDecl *ND, const WeakInfo &W) {
   if (W.getAlias()) { // clone decl, impersonate __attribute(weak,alias(...))
     IdentifierInfo *NDId = ND->getIdentifier();
+
+    // Append attribute on previous declaration only.
+    NamedDecl *Prev = LookupSingleName(TUScope, W.getAlias(), W.getLocation(),
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aokblast wrote:

```
void test1();
#pragma test1 = test2;
```

Prev = void test1();
ND = test2; This means we want to attach alias attributes to the Prev while the NDId is from test2.

https://github.com/llvm/llvm-project/pull/228809