[lld] [llvm] [hexagon] Bump the default version to v68 (PR #132304)

[Fangrui Song via llvm-commits]

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@@ -125,7 +125,7 @@ static cl::opt<bool>
 static cl::opt<bool> EnableHexagonCabac
   ("mcabac", cl::desc("tbd"), cl::init(false));
 
-static StringRef DefaultArch = "hexagonv60";
+static StringRef DefaultArch = "hexagonv68";
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MaskRay wrote:

`constexpr StringRef defaultArch`

https://github.com/llvm/llvm-project/pull/132304