Non functional change. Initialize var EnumVal to 0. (llvm#82987)

CodeGenInstruction has a new unsigned member EnumVal. It is not
initialized in either the class or the constructor.

llvm/utils/TableGen/CodeGenInstruction.h

@@ -301,7 +301,7 @@ class CodeGenInstruction {
   Record *InferredFrom;
 
   // The enum value assigned by CodeGenTarget::computeInstrsByEnum.
-  mutable unsigned EnumVal;
+  mutable unsigned EnumVal = 0;
 
   CodeGenInstruction(Record *R);