Go step by step. Cross-compiling for another architecture is not so simple...
First, before going for vncviewer, set up your toolchain:
https://kindlemodding.org/kindle-dev...equisites.html
Test your setup with the example project from the kindlemodding site.
For cloning use the recursive flag:
git clone --recursive
https://github.com/hwhw/kindlevncviewer.git
for building you might need to set the prefix for the toolchain. A bit difficult to say how to do it without trying.