[mythtv-users] Can't build fixes/30 from source on Gentoo

[mythtv]

I'm guessing someone must have built fixes/30 on Gentoo by now. I get 
the following error:

libavdevice/alsa.c: In function ‘ff_alsa_close’:
libavdevice/alsa.c:306:9: error: ‘CONFIG_ALSA_INDEV’ undeclared (first 
use in this function); did you mean ‘CONFIG_VALGRIND’?
      if (CONFIG_ALSA_INDEV)
          ^~~~~~~~~~~~~~~~~
          CONFIG_VALGRIND


If I remove alsa-lib from my machine to get ffmpeg to ignore it, then I 
get a different error:

libavdevice/avdevice.c: In function ‘avdevice_configuration’:
libavdevice/avdevice.c:72:12: error: ‘FFMPEG_CONFIGURATION’ undeclared 
(first use in this function); did you mean ‘FFMPEG_VERSION’?
      return FFMPEG_CONFIGURATION;
             ^~~~~~~~~~~~~~~~~~~~
             FFMPEG_VERSION


I'm on Gentoo, gcc 8.3.0. It fails pretty much immediately when trying 
to build.