The
tvheadend-git
package for Arch (in the AUR) builds H.265 support in by default, and links it to the system's libx265 rather than building a static version for Tvheadend. However, I'm not sure any repo packag's a binary with it built-in.
Your best bet is to just build it from scratch yourself. Just include
--enable-libx265 --disable-libx265_static
in your configure options. (Although, ensure you have the libx265 headers, first ;-)