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

[Nathan Chancellor 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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nathanchance wrote:

Done, I verified that the existing tests fail if I change it locally to `63`: 9cebddc37a53324b2fd643bf140b9978e92e5366

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