[clang] [Clang] fix parser recovery for invalid static_assert string messages (PR #187859)

[Corentin Jabot via cfe-commits]

================
@@ -980,7 +980,7 @@ Decl *Parser::ParseStaticAssertDeclaration(SourceLocation &DeclEnd) {
     if (getLangOpts().CPlusPlus11) {
       for (unsigned I = 0;; ++I) {
         const Token &T = GetLookAheadToken(I);
-        if (T.is(tok::r_paren))
+        if (T.isOneOf(tok::r_paren, tok::semi, tok::eof))
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cor3ntin wrote:

I agree with Aaron, this does not seem to be the right fix. 
The issue seems to be that `T.consumeClose()` return false on semicolon - It's weird but changing that is probably gonna hurt recovery in other places.

so the
```
if (T.consumeClose())
   return nullptr;
```

Fails to do its job - maybe we can check here `if(Tok.isNot(r_paren) || /*...*/`).
Not very elegant but better than anything that would involve change to Sema

For the diagnostic message in @AaronBallman's link, we could choose to display it only if `ParseConstantExpressionInExprEvalContext()` produces something valid.

https://github.com/llvm/llvm-project/pull/187859