Use writerStreaming() instead of writer() for stdout in helpgen and
main_build_data. The positional writer calls setEndPos/ftruncate in
end(), which fails on Windows when stdout is redirected via
captureStdOut() because ftruncate maps INVALID_PARAMETER to
FileTooBig. Streaming mode skips truncation entirely since stdout
is inherently a sequential stream.
Replace scandir with opendir/readdir plus qsort in framegen since
scandir is a POSIX extension not available on Windows.
