message: Log TF_POPLAR_FLAGS
  Summary:
  Add VLOG(1) for checking `TF_POPLAR_FLAGS` is set to expected values.
  Fix T46333
  Test Plan: CI
  Reviewers: babakk, vladimirm, gauthamg, #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved
  Maniphest Tasks: T46333
diff: @@ -31,6 +31,7 @@ limitations under the License.
  namespace xla {
  namespace poplarplugin {
  namespace {
  +static const char* const kEnvVarName = "TF_POPLAR_FLAGS";
  SyntheticDataCategory SyntheticDataCategoryFromName(absl::string_view name) {
  #define RETURN_CATEGORY_FOR_NAME(NAME, CATEGORY) \
  @@ -199,12 +200,13 @@ PoplarXlaFlags::PoplarXlaFlags() {
  "synthetic_data_categories", synthetic_data_category_hook,
  /*default*/ "", flag_usage["synthetic_data_categories"]));
  - xla::ParseFlagsFromEnvAndDieIfUnknown("TF_POPLAR_FLAGS", flag_list);
  + xla::ParseFlagsFromEnvAndDieIfUnknown(kEnvVarName, flag_list);
  // Store all the flags as a string.
  as_string = "";
  - if (const char* flag_buffer = std::getenv("TF_POPLAR_FLAGS")) {
  + if (const char* flag_buffer = std::getenv(kEnvVarName)) {
  as_string = flag_buffer;
  + VLOG(1) << kEnvVarName << " is set to '" << as_string << "'";
  }
  const auto invalid_synthetic_data_category =
  