Load C++ for functions?

I'm trying to link up a C++ project with postgres functions, the following code compiles (as C++):

extern "C" {
#include <postgres.h>
#include <fmgr.h>

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
};

extern "C" {
PG_FUNCTION_INFO_V1(pg_xversion);
};
extern "C" Datum pg_xversion(PG_FUNCTION_ARGS)
{
PG_RETURN_NULL();
}

But the CREATE FUNCTION gives the error:
ERROR: could not load library "/storage/Scripts/pgx/pgx.so": /storage/Scripts/pgx/pgx.so: undefined symbol: __gxx_personality_v0

Postgres is no doubt trying to load a C++ linked library as C - is there a way to fix this?