Omit the DataCount section unless it is required (#1312)

See #1189 and #1311. Even if bulk memory is enabled, it can be
convenient to omit the DataCount section for MVP compatibility.

This change only includes the DataCount section when an instruction
requires it; either `data.drop` or `memory.init`. It is also omitted if
there are no data segments.

Rather than doing a second pass on the instructions, this implementation
unconditionally writes the DataCount section, but removes it when it is
not needed. This required adding a function to truncate a stream
(Stream::Truncate).

0 files changed, 0 insertions, 0 deletions