These were left over from $FreeBSD$ removal.
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D42612
(cherry picked from commit 1ca63a8219b88b752b064d19bd3428c61dbcf1f9)
Create a stdlib/malloc to hold the definition of the malloc interface
(e.g., the Symbol.map file) and make jemalloc a subdirectory. This will
make it easier to integrate alternative allocators such as snmalloc
while making it clear that the current jemalloc symbols are the FreeBSD
API/ABI (for better or worse).
Suggested by: jrtc27
Reviewed by: jrtc27, emaste
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D41457