When compiling with clang, try adding -Qunused-arguments to the compiler
flags.
Something like
# Add -Qunused-arguments to CFLAGS if clang/clang++ is used.
.if ${CC:T:Mclang} == "clang" || ${CXX:T:Mclang++} == "clang++"
CFLAGS+= -Qunused-arguments
.endif
in /etc/make.conf should do it.
Regards!
--
Niclas Zeising