add extra sources for SVT-AV1 encoder plugin (#1480)

Author: farindk

libheif/plugins/CMakeLists.txt

@@ -66,7 +66,7 @@ set(AOM_ENCODER_extra_plugin_sources ../error.cc ../common_utils.cc ../common_ut
 plugin_compilation(aomenc AOM AOM_ENCODER_FOUND AOM_ENCODER AOM_ENCODER)
 
 set(SvtEnc_sources encoder_svt.cc encoder_svt.h)
-set(SvtEnc_extra_plugin_sources)
+set(SvtEnc_extra_plugin_sources ../common_utils.cc ../common_utils.h)
 plugin_compilation(svtenc SvtEnc SvtEnc_FOUND SvtEnc SvtEnc)
 
 set(RAV1E_sources encoder_rav1e.cc encoder_rav1e.h)