fr: Fix the linking of the test and use $(LIBRARY_DL) for linking

On Ubuntu 13.04 the build was failing on the OBS with:
/usr/bin/ld: fr_test.o: undefined reference to symbol 'dlsym@@GLIBC_2.2.5'
/usr/bin/ld: note: 'dlsym@@GLIBC_2.2.5' is defined in DSO /lib/x86_64-linux-gnu/libdl.so.2 so try adding it to the linker command line
/lib/x86_64-linux-gnu/libdl.so.2: could not read symbols: Invalid operation
collect2: error: ld returned 1 exit status
1 file changed