Are these flags set in standard perl build for ubuntu?

On the system perl on my Ubuntu (12.04LTS), useithreads is defined, but usemymalloc is not:

sisyphus@sisyphus5-desktop:~$ perl -V:usemymalloc
usemymalloc='n';
sisyphus@sisyphus5-desktop:~$ perl -V:useithreads
useithreads='define';
sisyphus@sisyphus5-desktop:~$
[download]

(You'll want "usemymalloc='y'".)
I have built some other perls, but none with -Dusemymalloc.
Maybe you should build one ?

Cheers,
Rob