package/tvheadend: fix build error with c++ disabled

The vp8 encoder depends on c++ support since commit
06a1a05b55aa64720d4ede9b07c385cc8f06625d

src/transcoding/codec/codecs/libs/libvpx.c:23:10: fatal error: vpx/vp8cx.h: No such file or directory
   23 | #include <vpx/vp8cx.h>

Fixes:
http://autobuild.buildroot.net/results/152/152dec2f7148a23fa1a434d2c6ad31de6d1b2466/
http://autobuild.buildroot.net/results/009/0090b100eca4f94d2f0081ce0db7ff9b4ae0ca79/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/tvheadend/Config.in

@@ -66,7 +66,8 @@ config BR2_PACKAGE_TVHEADEND_TRANSCODING
 	select BR2_PACKAGE_FFMPEG_AVRESAMPLE
 	select BR2_PACKAGE_FFMPEG_GPL # needed for x264 support
 	select BR2_PACKAGE_FFMPEG_SWSCALE
-	select BR2_PACKAGE_LIBVPX
+	# vp8 encoder needs c++
+	select BR2_PACKAGE_LIBVPX if BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_X264
 	help
 	  Enable transcoding support.

package/tvheadend/tvheadend.mk

@@ -47,6 +47,12 @@ TVHEADEND_DEPENDENCIES += rpi-userland
 else
 TVHEADEND_CONF_OPTS += --disable-omx
 endif
+ifeq ($(BR2_PACKAGE_LIBVPX)$(BR2_INSTALL_LIBSTDCPP),yy)
+TVHEADEND_CONF_OPTS += --enable-libvpx
+TVHEADEND_DEPENDENCIES += libvpx
+else
+TVHEADEND_CONF_OPTS += --disable-libvpx
+endif
 ifeq ($(BR2_PACKAGE_X265),y)
 TVHEADEND_CONF_OPTS += --enable-libx265
 TVHEADEND_DEPENDENCIES += x265
@@ -59,6 +65,7 @@ TVHEADEND_CONF_OPTS += \
 	--disable-libopus \
 	--disable-omx \
 	--disable-vaapi \
+	--disable-libvpx \
 	--disable-libx264 \
 	--disable-libx265
 endif