[clang] [clang] Introduce '-fint64-is-long-long' (PR #234780)

[Hubert Tong via cfe-commits]

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@@ -562,6 +562,9 @@ void TargetInfo::adjust(DiagnosticsEngine &Diags, LangOptions &Opts,
     }
   }
 
+  if (Opts.Int64LongLong)
+    Int64Type = SignedLongLong;
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hubert-reinterpretcast wrote:

> It seems like if this is unsupported, it would be better to report the error to the user, rather than having an internal assertion but maybe checking this all the time is too expensive?

The code looks good. The behaviour of the error-path being not testable at this time is unfortunate; but, as the change merely uses an existing diagnostic, I guess we are okay.

https://github.com/llvm/llvm-project/pull/234780