message: [XLA] Allow match::Op().WithCustomCallTarget({x, y, z}).
  Previously you could only do WithCustomCallTarget(x).  This change allows you
  to match a custom call with one of a list of targets.
diff: @@ -1208,29 +1208,41 @@ class HloInstructionPatternOpcodeImpl {
  };
  // An HloInstructionPattern implementation that matches only if the instruction
  -// has a given custom call target.
  +// has one of a given list of custom call targets.
  class HloInstructionCustomCallTargetImpl {
  public:
  explicit HloInstructionCustomCallTargetImpl(
  - absl::string_view custom_call_target)
  - : custom_call_target_(custom_call_target) {}
  + absl::Span<const absl::string_view> custom_call_targets)
  + : custom_call_targets_(custom_call_targets.begin(),
  + custom_call_targets.end()) {}
  bool Match(const ::xla::HloInstruction* inst, MatchOption option) const {
  if (inst->opcode() != HloOpcode::kCustomCall ||
  - inst->custom_call_target() != custom_call_target_) {
  + !absl::c_linear_search(custom_call_targets_,
  + inst->custom_call_target())) {
  + if (custom_call_targets_.size() == 1) {
  EXPLAIN << "HloInstruction is not a custom call with a target '"
  - << custom_call_target_ << "'";
  + << custom_call_targets_.front() << "'";
  + } else {
  + EXPLAIN << "HloInstruction is not a custom call with a target in {"
  + << absl::StrJoin(custom_call_targets_, ", ") << "}";
  + }
  return false;
  }
  return true;
  }
  void DescribeTo(std::ostream* os, int64 indent = 0) const {
  - *os << "custom call with target '" << custom_call_target_ << "'";
  + if (custom_call_targets_.size() == 1) {
  + *os << "custom call with target '" << custom_call_targets_.front() << "'";
  + } else {
  + *os << "custom call with target in {"
  + << absl::StrJoin(custom_call_targets_, ", ") << "}";
  + }
  }
  private:
  - std::string custom_call_target_;
  + absl::InlinedVector<std::string, 1> custom_call_targets_;
  };
  // An HloInstructionPattern implementation that matches only if the instruction
  @@ -1812,7 +1824,13 @@ class HloInstructionPattern {
  // Modifies the pattern to match only the custom call with a given target.
  auto WithCustomCallTarget(absl::string_view custom_call_target) const {
  - return AppendImpl(HloInstructionCustomCallTargetImpl(custom_call_target));
  + return AppendImpl(HloInstructionCustomCallTargetImpl({custom_call_target}));
  + }
  +
  + // Modifies the pattern to match a custom call with one of the given targets.
  + auto WithCustomCallTarget(
  + absl::Span<const absl::string_view> custom_call_targets) const {
  + return AppendImpl(HloInstructionCustomCallTargetImpl(custom_call_targets));
  }
  auto WithNumOperands(int64 num_operands) const {
  