Bug 1830986 - Fix 32-bit builds.

  // Try to keep the size of StringBuilder close to a jemalloc bucket size (the

  // 16kb one in this case).

  static constexpr uint32_t TARGET_SIZE = 16 * 1024;

  static const uint32_t STRING_BUFFER_UNITS = TARGET_SIZE / sizeof(Unit) - 1;

  // The number of units we need to remove from the inline buffer so that the

  // rest of the builder members fit. A more precise approach would be to

  // calculate that extra size and use (TARGET_SIZE - OTHER_SIZE) / sizeof(Unit)

  // or so, but this is simpler.

  static constexpr uint32_t PADDING_UNITS = sizeof(void*) == 8 ? 1 : 2;

  static constexpr uint32_t STRING_BUFFER_UNITS =

      TARGET_SIZE / sizeof(Unit) - PADDING_UNITS;

  StringBuilder() : mLast(this), mLength(0) { MOZ_COUNT_CTOR(StringBuilder); }