This supersedes -std=gnu99, and enables C11 atomics.

Do not call s2u() during alloc_size computation, since any necessary
ceiling increase is taken care of later by extent_first_best_fit() -->
extent_size_quantize_ceil(), and the s2u() call may erroneously cause a
higher quantization result.

Remove an overly strict overflow check that was added in
4a785213 (Fix extent_recycle()'s
cache-oblivious padding support.).

Add padding *after* computing the size class, so that the optimal size
class isn't skipped during search for a usable extent.  This regression
was caused by b46261d5 (Implement
cache-oblivious support for huge size classes.).

Add an "over-size" extent heap in which to store extents which exceed
the maximum size class (plus cache-oblivious padding, if enabled).
Remove psz2ind_clamp() and use psz2ind() instead so that trying to
allocate the maximum size class can in principle succeed.  In practice,
this allows assertions to hold so that OOM errors can be successfully
generated.

Fix extent_alloc_cache[_locked]() to support decommitted allocation, and
use this ability in arena_stash_dirty(), so that decommitted extents are
not needlessly committed during purging.  In practice this does not
happen on any currently supported systems, because both extent merging
and decommit must be implemented; all supported systems implement one
xor the other.

Treat it exactly like Linux since they both use GNU libc.

rtree_node_init spinlocks the node, allocates, and then sets the node.
This is under heavy contention at the top of the tree if many threads
start to allocate at the same time.

Instead, take a per-rtree sleeping mutex to reduce spinning.  Tested
both pthreads and osx OSSpinLock, and both reduce spinning adequately

Previous benchmark time:
./ttest1 500 100
~15s

New benchmark time:
./ttest1 500 100
.57s

This resolves #485.

OS X 10.12 deprecated OSSpinLock; os_unfair_lock is the recommended
replacement.

Fix zone_force_unlock() to reinitialize, rather than unlocking mutexes,
since OS X 10.12 cannot tolerate a child unlocking mutexes that were
locked by its parent.

Refactor; this was a side effect of experimenting with zone
{de,re}registration during fork(2).

_exit(2) is async-signal-safe, whereas exit(3) is not.

Monitoring thread creation is unimplemented for Windows, which means
lazy-lock cannot function correctly.

This resolves #310.

Fix and clean up various malloc_stats_print() issues caused by
0ba5b9b6 (Add "J" (JSON) support to
malloc_stats_print().).

This resolves #474.

This resolves #480.

This resolves #396.

The raw clock variant is slow (even relative to plain CLOCK_MONOTONIC),
whereas the coarse clock variant is faster than CLOCK_MONOTONIC, but
still has resolution (~1ms) that is adequate for our purposes.

This resolves #479.

Some applications wrap various system calls, and if they call the
allocator in their wrappers, unexpected reentry can result.  This is not
a general solution (many other syscalls are spread throughout the code),
but this resolves a bootstrapping issue that is apparently common.

This resolves #443.

This works around malloc_conf not being properly initialized by at least
the cygwin toolchain.  Prior build system changes to use
-Wl,--[no-]whole-archive may be necessary for malloc_conf resolution to
work properly as a non-weak symbol (not tested).

This is generally correct (no need for weak symbols since no jemalloc
library is involved in the link phase), and avoids linking problems
(apparently unininitialized non-NULL malloc_conf) when using cygwin with
gcc.

glibc defines its malloc implementation with several weak and strong
symbols:

strong_alias (__libc_calloc, __calloc) weak_alias (__libc_calloc, calloc)
strong_alias (__libc_free, __cfree) weak_alias (__libc_free, cfree)
strong_alias (__libc_free, __free) strong_alias (__libc_free, free)
strong_alias (__libc_malloc, __malloc) strong_alias (__libc_malloc, malloc)

The issue is not with the weak symbols, but that other parts of glibc
depend on __libc_malloc explicitly.  Defining them in terms of jemalloc
API's allows the linker to drop glibc's malloc.o completely from the link,
and static linking no longer results in symbol collisions.

Another wrinkle: jemalloc during initialization calls sysconf to
get the number of CPU's.  GLIBC allocates for the first time before
setting up isspace (and other related) tables, which are used by
sysconf.  Instead, use the pthread API to get the number of
CPUs with GLIBC, which seems to work.

This resolves #442.

This is intended to drop memory usage to a level that AppVeyor test
instances can handle.

This resolves #393.

This resolves #393.

This resolves #393.

Use the correct level metadata when allocating child nodes so that leaf
nodes don't end up over-sized (2^16 elements vs 2^4 elements).

This avoids warnings in some cases, and is otherwise generally good
hygiene.

Rather than relying on two's complement negation for alignment mask
generation, use bitwise not and addition.  This dodges warnings from
MSVC, and should be strength-reduced by compiler optimization anyway.

This fixes warnings when building with MSVC.

Conditionalize use of --whole-archive on the platform plus compiler,
rather than on the ABI.  This fixes a regression caused by
7b24c6e5 (Use --whole-archive when
linking integration tests on MinGW.).