The following discussion is meant to explain the difference between hosts and targets. Defines and include files needed to build on the host are host support.
Examples are tty support, system defined types, host byte order, host float format.
Defines and information needed to handle the target format are target dependent. Examples are the stack frame format, instruction set, breakpoint instruction, registers, and how to set up and tear down the stack to call a function. Information that is only needed when the host and target are the same, is native dependent. The dependent information in GDB is organized into files by naming conventions. At this writing, most supported hosts have had their host and native dependencies sorted out properly.