aui.boot: appears completely silent while building AUI

This is healthy behaviour of aui.boot; however, it misleads newcomers into thinking that build is stuck.

After [logging about building](https://github.com/aui-framework/aui/blob/f6a83191637d4be02293b99770dc5812d6bcfc54/aui.boot.cmake#L994), `aui.boot` invokes build procedure by subsequent `execute_process` call, which is instructed to dump logs to `build.log`. After `execute_process` is completed, aui.boot dumps logs from that file using `_auib_dump_with_prefix` to maintain prefix on each line of the dumped log file.

This results into chunked output, when build output is not being filled in the process, instead full file is dumped at the end.

The task is to get rid of chunkiness, while preserving both `build.log` and output prefixing.

Read aui.boot.cmake around line 994, then trace the execute_process call, build.log handling, and _auib_dump_with_prefix. Run an AUI build to observe the current chunked output. Done means build output appears continuously while build.log is still preserved and every displayed line retains its prefix.

Written by the indexing model from the issue text.