aom_dsp_rtcd_defs.pl checks only whether this key is present in the config, not whether it is set to true or not. Our script sets CONFIG_FOO=no for disabled options, while the upstream build system omits them, resulting in extra symbol declarations the build will never define.
Work around this by stripping the offending disabled config key if it is disabled.
This is a port of the libvpx scripts, themselves a port of Chromium's scripts to generate an external build description using hooks in the upstream configure and make scripts. The libaom library is a fork of libvpx so we can use a similar approach.
The upstream source is located in $(topsrc_dir)/third_party/aom but the build description and any patches are under the media directory with the other codecs, similar to how zlib works. Config files and headers generated by the upstream build system are also under $(topsrc_dir)/media/libaom/.
