Fix building tests with gcc48

/usr/local/bin/ld: pkg_printf.o: undefined reference to symbol 'sbuf_putc'
/usr/local/bin/ld: note: 'sbuf_putc' is defined in DSO //lib/libsbuf.so.5 so try adding it to the linker command line
//lib/libsbuf.so.5: could not read symbols: Invalid operation