When trying to link against the library provided by devel/grpc there is undefined symbols to gpr_log.
readelf -s ../../work/stage/usr/local/lib/libgrpc.so | grep gpr_log
36: 0000000000000000 0 FUNC GLOBAL DEFAULT UND gpr_log
This causes programs which link with libgrpc to fail which need gpr_log.
To reproduce just build from the port tree.
I've solved the linking as they are defined in lib/libgpr.so however as no pc file are provided, buidl system can't get the correct linking order. -lgpr -lgrpc.
Maybe the port should provide some libdata/pkgconfig/*.pc files.