Port sysklogd to NuttX

[xiaoxiang781216]

https://github.com/apache/incubator-nuttx

[troglobit]

Hi great contribution! Since this is the first NuttX contribution to sysklogd, maybe you would like to describe the changes you've made? There are lots of #ifdefs sprinkled in that have no comments, so please let us know what they do and what your intent is to achieve with these changes -- after all, there may be better ways to achieve what you want. I may know of a few already, but I'd rather hear from you first than presume to guess.

[troglobit]

For instance, maybe it would be a good idea to also add a GitHub Action to build for NuttX, just to ensure we don't introduce any obvious regressions to your port, going forward.

[troglobit]

OK, no feedback on my questions, so I'm merging this with the provision of not taking responsibility for any regressions the project may introduce in the NuttX port.

Thank you for your contribution! :-)