jemalloc: Import version 5.2.1

Create a new vendor branch for jemalloc, using the following for future
reference:

% git worktree add --orphan -b vendor/jemalloc ../vendors/jemalloc
% cd ../vendors/jemalloc
% git checkout -b vendor/jemalloc

% cd ../../upstreams
% git clone [email protected]:jemalloc/jemalloc.git
% cd jemalloc
% git checkout 5.2.1 # hash ea6b3e973b477b8061e0076bb257dbd7f3faa756

% cp -r * ../../vendors/jemalloc
% cd ../../vendors/jemalloc
% autoconf
% ./configure --enable-autoconf --with-version=5.2.1-0-gea6b3e973b477b8061e0076bb257dbd7f3faa756
% git add *
% git commit -m<this message>
% git tag -a vendor/jemalloc/5.2.1
% git push --follow --set-upstream freebsd vendor/jemalloc

Note: This purposely doesn't thin the vendor branch. That will be done
in the next step to create the merge commit that boostraps future
imports.

Sponsored by:		Netflix

Author: bsdimp

COPYING

@@ -0,0 +1,27 @@
+Unless otherwise specified, files in the jemalloc source distribution are
+subject to the following license:
+--------------------------------------------------------------------------------
+Copyright (C) 2002-present Jason Evans <[email protected]>.
+All rights reserved.
+Copyright (C) 2007-2012 Mozilla Foundation.  All rights reserved.
+Copyright (C) 2009-present Facebook, Inc.  All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+1. Redistributions of source code must retain the above copyright notice(s),
+   this list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright notice(s),
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY EXPRESS
+OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
+EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+--------------------------------------------------------------------------------