$ sh Configure -de -Dusedevel -Dusethreads

Beginning of configuration questions for perl5.

[...]

Perl can be built to take advantage of threads on some systems.
To do so, Configure can be run with -Dusethreads.

Note that Perl built with threading support runs slightly slower
and uses more memory than plain Perl. The current implementation
is believed to be stable, but it is fairly new, and so should be
treated with caution.

If this doesn't make any sense to you, just accept the default 'n'.
Build a threading Perl? [n]

##</code><code>##

$ perl -Ilib -V:config_args -V:useithreads
config_args='-de -Dusedevel -Dusethreads';
useithreads='undef';

$ perl -Ilib -E'use threads; say "threaded"'
This Perl not built to support threads
Compilation failed in require at -e line 1.
BEGIN failed--compilation aborted at -e line 1.