GitLab

Detail:
* Rewrite Makefile to use CApp shared makefile
* #includes use CLX/ prefix explicitly to avoid having to set a host
  OS-specific -I switch
* Rather than passing in -DRISCOS for all targets, use compiler predefine
  __riscos to select target OS-specific code paths only when necessary
* Remove toolchain-specific -Wc switch (it wasn't suppressing any warnings
  anyway)
* Add a couple of #includes needed to make it compile on Linux