Update Makefile for libtorrent

Fix for the -fPIC error:


cc1: warning: command line option "-ftemplate-depth-100" is valid for C++/ObjC++ but not for C
x86_64-linux-gnu-gcc: -lpthread: linker input file unused because linking not done
  CXX      asio_ssl.lo
  CXXLD    libtorrent-rasterbar.la
/root/spksrc/toolchains/syno-cedarview/work/x86_64-linux-gnu/bin/../lib/gcc/x86_64-linux-gnu/4.2.0/../../../../x86_64-linux-gnu/bin/ld: .libs/chained_buffer.o: relocation R_X86_64_PC32 against `boost::function1<void, char*>::clear()' can not be used when making a shared object; recompile with -fPIC
/root/spksrc/toolchains/syno-cedarview/work/x86_64-linux-gnu/bin/../lib/gcc/x86_64-linux-gnu/4.2.0/../../../../x86_64-linux-gnu/bin/ld: final link failed: Bad value
collect2: ld returned 1 exit status


as reported on http://sourceforge.net/mailarchive/message.php?msg_id=30296008