For the tinc command’s shell functionality, tinc uses the readline library.
If this library is not installed, you will get an error when running the configure script. You can either install a suitable readline library, or disable all functionality that depends on a readline library by using the --disable-readline option when running the configure script.
You can use your operating system’s package manager to install this if available. Make sure you install the development AND runtime versions of this package.
If you have to install libreadline manually, you can get the source code from https://www.gnu.org/software/readline/. Instructions on how to configure, build and install this package are included within the package. Please make sure you build development and runtime libraries (which is the default).