Firefox 68 on POWER

Firefox 68 is out. I haven't had a chance to exhaustively test it on my ppc64le Talos II due to business trips and some family obligations, but on cursory testing the browser seems to function normally. Unfortunately our last minute latest workaround for (what is now clearly) a compiler bug in bug 1512162 did not make release, so you'll need to add it if you build from source; without it, some optimization levels may crash or behave adversely. We have not yet narrowed down the issue in gcc and on my last check clang still can't build the browser fully. Fortunately the fix did land on the new Extended Support Release 68, so individuals who prefer the ESR should be able to build as-is from there, and the fix also does not appear to be necessary on big-endian. Thanks to Dan Horák's usual quick work, the patch is also in the standard Fedora packages. The configurations I'm using are unchanged from Firefox 67.