mimalloc: un-break dynamic linking
mimalloc: un-break dynamic linking

Previous versions of the build assumed libmimalloc.so would be a hard
copy of mimalloc-secure.so iff secureBuild == true, but in 1.1.0 and
later it seems libmimalloc.so is a symlink to the -secure variant. This
apparently rectifies some behavior I noticed that was strange
previously.

This breakage wasn't caught because the 1.1.0 update was automatic in
5596317d4; there should be a checkPhase to ensure this doesn't happen
again...

Signed-off-by: Austin Seipp <48c905ac3851f382b914247d97dd93273d5ff555@pobox.com>

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