message: Simplify UUID constructors
  Summary: This remove a small amount of duplicated code.
  Reviewers: clayborg, zturner, davide
  Subscribers: lldb-commits
diff: namespace lldb_private {
  -UUID::UUID() : m_num_uuid_bytes(16) { ::memset(m_uuid, 0, sizeof(m_uuid)); }
  +UUID::UUID() { Clear(); }
  UUID::UUID(const UUID &rhs) {
  - m_num_uuid_bytes = rhs.m_num_uuid_bytes;
  - ::memcpy(m_uuid, rhs.m_uuid, sizeof(m_uuid));
  + SetBytes(rhs.m_uuid, rhs.m_num_uuid_bytes);
  }
  UUID::UUID(const void *uuid_bytes, uint32_t num_uuid_bytes) {
  