Fix link of snapwatchd on Ubuntu raring

snapwatchd fails to link a shared .so with -shared:

  /usr/bin/ld: xslib.o: relocation R_X86_64_32 against `.rodata.str1.1'
  can not be used when making a shared object
  xslib.o: could not read symbols: Bad value

We need to explicitly compile our objects as position-independent
code with -fPIC

Signed-off-by: David Scott <dave.scott@eu.citrix.com>