vpx: Build broken for libvpx 1.8.0
This is happening on macOS with libvpx 1.8.0 installed using HomeBrew:
../subprojects/gst-plugins-good/ext/vpx/gstvpxdec.c:65:15: error: use of undeclared identifier 'VP8_DEBUG_TXT_FRAME_INFO'
{C_FLAGS (VP8_DEBUG_TXT_FRAME_INFO),
^
../subprojects/gst-plugins-good/ext/vpx/gstvpxdec.c:68:15: error: use of undeclared identifier 'VP8_DEBUG_TXT_MBLK_MODES'
{C_FLAGS (VP8_DEBUG_TXT_MBLK_MODES),
^
../subprojects/gst-plugins-good/ext/vpx/gstvpxdec.c:71:15: error: use of undeclared identifier 'VP8_DEBUG_TXT_DC_DIFF'
{C_FLAGS (VP8_DEBUG_TXT_DC_DIFF),
^
../subprojects/gst-plugins-good/ext/vpx/gstvpxdec.c:74:15: error: use of undeclared identifier 'VP8_DEBUG_TXT_RATE_INFO'
{C_FLAGS (VP8_DEBUG_TXT_RATE_INFO),
^