[build] Rename `build/unix/ftconfig.in' to `ftconfig.h.in'.

Since we are no longer limited to 8.3 file names, it is simpler to
follow the usual conventions for template files.

* builds/unix/ftconfig.in: Renamed to...
* builds/unix/ftconfig.h.in: ...this.

* CMakeLists.txt, builds/unix/configure.raw: Updated.
4 files changed