users: workaround build failure

x86_64-suse-linux/bin/ld: libusers_internal.a(mocs_compilation.cpp.o):
  relocation R_X86_64_32 against symbol `_ZN6Config16staticMetaObjectE'
  can not be used when making a shared object; recompile with -fPIC
x86_64-suse-linux/bin/ld: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status