[mlir][llvm] Add a convenience builder to BrOp

[Mogball]

Summary

This builder takes no successor arguments.

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

 // Terminators.
 def LLVM_BrOp : LLVM_TerminatorOp<"br",
     [DeclareOpInterfaceMethods<BranchOpInterface>, Pure]> {
   let arguments = (ins Variadic<LLVM_Type>:$destOperands);
   let successors = (successor AnySuccessor:$dest);
   let assemblyFormat = [{
     $dest (`(` $destOperands^ `:` type($destOperands) `)`)? attr-dict
   }];
-  let builders = [LLVM_TerminatorPassthroughOpBuilder];
+  let builders = [
+    OpBuilder<(ins "Block *":$dest), [{
+      build($_builder, $_state, ValueRange(), dest);
+    }]>,
+    LLVM_TerminatorPassthroughOpBuilder
+  ];
 }
 def LLVM_CondBrOp : LLVM_TerminatorOp<"cond_br",
     [AttrSizedOperandSegments, DeclareOpInterfaceMethods<BranchOpInterface>,
      Pure]> {
   let arguments = (ins I1:$condition,
                    Variadic<LLVM_Type>:$trueDestOperands,
                    Variadic<LLVM_Type>:$falseDestOperands,
                    OptionalAttr<ElementsAttr>:$branch_weights);