We're not actually using it, and it messes up with the zone allocator in
mozjemalloc after fork(). See the lengthy analysis in
https://bugzilla.mozilla.org/show_bug.cgi?id=1424709#c34 and following.
--HG--
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extra : intermediate-source : 45c5d467a46077dcc3ccd59feafd0c2784432fef
extra : source : bf1efa161edb20a83fe8db2f96c51f4e66880153