Firefox 107 on POWER

Firefox 107 is out, a modest update, though there are some developer-facing changes. As before linking still requires Dan Horák's patch from bug 1775202 or the browser won't link on 64-bit Power ISA (alternatively put --disable-webrtc in your .mozconfig if you don't need WebRTC). Otherwise the build works with the .mozconfigs from Firefox 105 and the PGO-LTO patch from Firefox 101.