Add USES=compiler:c++11-lang to fix build on GCC architectures.
Don't add -L${OPENSSLLIB} unconditionally, do it only when SSL library from ports is used. The reason is that adding -L/usr/lib makes ports GCC want to link to libstdc++ from /usr/lib, not from /usr/local/lib/gcc8.
Tested on powerpc64 and amd64.