Going through the system zone allocator for every call to realloc/free
on OSX is costly, because the zone allocator needs to first verify that
the allocations do belong to the allocator it invokes (which ends up
calling jemalloc's malloc_usable_size), which is unnecessary when we
expect the allocations to belong to jemalloc.

So, we export the malloc/realloc/free/etc. symbols from
libmozglue.dylib, such that libraries and programs linked against it
call directly into jemalloc instead of going through the system zone
allocator, effectively shortcutting the allocator verification.

The risk is that some things in Gecko try to realloc/free pointers it
got from system libraries, if those were allocated with a system zone
that is not jemalloc.

--HG--
extra : rebase_source : ee0b29e1275176f52e64f4648dfa7ce25d61292e