[Sparc] Tweak r255668: Use llvm_unreachable.

llvm-svn: 255698
diff --git a/llvm/lib/Target/Sparc/SparcISelLowering.cpp b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
index 47c8c3a..5e70ffe 100644
--- a/llvm/lib/Target/Sparc/SparcISelLowering.cpp
+++ b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
@@ -527,7 +527,7 @@
                          "pass indirectly");
     } else {
       // We shouldn't see any other value types here.
-      assert(false && "Unexpected ValVT encountered in frame lowering.");
+      llvm_unreachable("Unexpected ValVT encountered in frame lowering.");
     }
     InVals.push_back(Load);
   }