Log message:
Import jemalloc-3.6.0 as wip/jemalloc.

jemalloc is a general purpose malloc(3) implementation that emphasizes
fragmentation avoidance and scalable concurrency support.

jemalloc first came into use as the FreeBSD libc allocator in 2005.
In 2010 jemalloc development efforts broadened to include developer support
features such as heap profiling, Valgrind integration, and
extensive monitoring/tuning hooks.
Ongoing development efforts trend toward making jemalloc among the best
allocators for a broad range of demanding applications, and
eliminating/mitigating weaknesses that have practical repercussions
for real world applications.