When the tranisiton to perl-cross occured, the threading define
seems to have been missed. The perl tests for threading where
simply skipped, so there was no direct failures. This was verified
by running perl ptest before and after the change to see PASS vs SKIP
results of threaded related tests.
NOTE: Perl officially discourges the use of threads, so this
functionality maybe depercated in the future [0][1]
v2: adds the usethreads to native and nativesdk. This was tested by
builing postresql and rrdtool which use perl and automake.
