libroot/posix: Enable OpenBSD malloc by default.

jam HaikuDepot with nothing to do, best of many runs:

hoard2
real    0m3.519s
user    0m3.348s
sys     0m0.159s

openbsd
real    0m3.481s
user    0m3.327s
sys     0m0.147s

time printf "continue\nsave-report\nquit\nk\n" | Debugger -c Debugger -s 1000

hoard2
real    0m2.295s
user    0m2.505s
sys     0m0.128s

openbsd
real    0m2.896s
user    0m2.809s
sys     0m0.579s

The performance difference in Debugger is due to OpenBSD malloc
actually decommitting memory. If we disable decommit, then
OpenBSD malloc is faster than hoard2 in this case also.

In some particular cases this is a huge speedup. For example, the link
of the "lto-dump" program in GCC seems to hit a pathological case in
hoard2 and our glue code for it; with hoard2 it takes around 23 seconds,
but with this allocator it takes only 2 seconds (!). Overall the
performance difference is much more modest, though.

Overall, system memory usage seems to be up about ~5% (318 MB -> 334 MB
just after boot), and that seems to mostly be due to the allocator
filling its initial caches faster when allocations occur, rather than
lazily allocating.

Change-Id: I071d8f76fbbfa11547bd6da6bf649d111414e780
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8974
Reviewed-by: waddlesplash <[email protected]>
Haiku-Format: Haiku-format Bot <[email protected]>
Tested-by: Commit checker robot <[email protected]>

src/system/libroot/posix/malloc/Jamfile

@@ -1,4 +1,5 @@
 SubDir HAIKU_TOP src system libroot posix malloc ;
 
 HaikuSubInclude debug ;
-HaikuSubInclude hoard2 ;
+#HaikuSubInclude hoard2 ;
+HaikuSubInclude openbsd ;