build: Detect when OpenFEC is built without some codecs

Earlier we required that OpenFEC should be always built with
both rs8m and ldpc enabled.

Now we updated to OpenFEC 1.4.2.11, which provides cmake options
to disable some codec. We detect it and don't use disabled codecs.

src/internal_modules/roc_fec/codec_map.cpp

@@ -18,6 +18,10 @@
 #include "roc_fec/openfec_encoder.h"
 #endif // ROC_TARGET_OPENFEC
 
+extern "C" {
+#include <of_openfec_api.h>
+}
+
 namespace roc {
 namespace fec {