Installing packages using ports after freebsd-update doesn't work on amd64

[Sorin Panca]

After upgrading the system using freebsd-update from 6.3-RELEASE to
7.0-RELEASE and after that, from 7.0 to 7.1 trying to install
ports-mgmt/portupgrade fails at ruby18 with the following message:

cc -shared -Wl,-soname,libruby18.so.18  array.o  bignum.o  class.o
compar.o  dir.o  dln.o  enum.o  error.o  eval.o  file.o  gc.o  hash.o
inits.o  io.o  marshal.o  math.o  numeric.o  object.o  pack.o  parse.o
process.o  prec.o  random.o  range.o  re.o  regex.o  ruby.o  signal.o
sprintf.o  st.o  string.o  struct.o  time.o  util.o  variable.o
version.o   dmyext.o -lcrypt -lm  -rpath=/usr/lib:/usr/local/lib
-pthread  -o libruby18.so.18
/usr/bin/ld: /usr/lib/libpthread.a(thr_syscalls.o): relocation
R_X86_64_32S can not be used when making a shared object; recompile with
-fPIC
/usr/lib/libpthread.a: could not read symbols: Bad value
*** Error code 1

I added CFLAGS?= -O2 -fPIC -pipe to /etc/make.conf but the problem persists.

I didn't activate pthread support for ruby18.

Any ideas on what's going wrong here?

Thank you!
Sorin.