message: The i1 argument is actually named "is_zero_undef" which we want to be false.
  Fixes the test failures that showed up on mac.
diff: @@ -2420,14 +2420,11 @@ impl FunctionCodeGenerator<CodegenError> for LLVMFunctionCodeGenerator {
  }
  Operator::I32Clz => {
  let input = state.pop1()?;
  - let ensure_defined_zero = intrinsics
  - .i1_ty
  - .const_int(1 as u64, false)
  - .as_basic_value_enum();
  + let is_zero_undef = intrinsics.i1_zero.as_basic_value_enum();
  let res = builder
  .build_call(
  intrinsics.ctlz_i32,
  - &[input, ensure_defined_zero],
  + &[input, is_zero_undef],
  &state.var_name(),
  )
  .try_as_basic_value()
  @@ -2437,14 +2434,11 @@ impl FunctionCodeGenerator<CodegenError> for LLVMFunctionCodeGenerator {
  }
  Operator::I64Clz => {
  let input = state.pop1()?;
  - let ensure_defined_zero = intrinsics
  - .i1_ty
  - .const_int(1 as u64, false)
  - .as_basic_value_enum();
  + let is_zero_undef = intrinsics.i1_zero.as_basic_value_enum();
  let res = builder
  .build_call(
  intrinsics.ctlz_i64,
  - &[input, ensure_defined_zero],
  + &[input, is_zero_undef],
  &state.var_name(),
  )
  .try_as_basic_value()
  @@ -2454,14 +2448,11 @@ impl FunctionCodeGenerator<CodegenError> for LLVMFunctionCodeGenerator {
  }
  Operator::I32Ctz => {
  let input = state.pop1()?;
  - let ensure_defined_zero = intrinsics
  - .i1_ty
  - .const_int(1 as u64, false)
  - .as_basic_value_enum();
  + let is_zero_undef = intrinsics.i1_zero.as_basic_value_enum();
  let res = builder
  .build_call(
  intrinsics.cttz_i32,
  - &[input, ensure_defined_zero],
  + &[input, is_zero_undef],
  &state.var_name(),
  )
  .try_as_basic_value()
  @@ -2471,14 +2462,11 @@ impl FunctionCodeGenerator<CodegenError> for LLVMFunctionCodeGenerator {
  }
  Operator::I64Ctz => {
  let input = state.pop1()?;
  - let ensure_defined_zero = intrinsics
  - .i1_ty
  - .const_int(1 as u64, false)
  - .as_basic_value_enum();
  + let is_zero_undef = intrinsics.i1_zero.as_basic_value_enum();
  let res = builder
  .build_call(
  intrinsics.cttz_i64,
  - &[input, ensure_defined_zero],
  + &[input, is_zero_undef],
  &state.var_name(),
  )
  .try_as_basic_value()
  