Port to FreeBSD.

Use FreeBSD-specific functions (_pthread_mutex_init_calloc_cb(),
_malloc_{pre,post}fork()) to avoid bootstrapping issues due to
allocation in libc and libthr.

Add malloc_strtoumax() and use it instead of strtoul().  Disable
validation code in malloc_vsnprintf() and malloc_strtoumax() until
jemalloc is initialized.  This is necessary because locale
initialization causes allocation for both vsnprintf() and strtoumax().

Force the lazy-lock feature on in order to avoid pthread_self(),
because it causes allocation.

Use syscall(SYS_write, ...) rather than write(...), because libthr wraps
write() and causes allocation.  Without this workaround, it would not be
possible to print error messages in malloc_conf_init() without
substantially reworking bootstrapping.

Fix choose_arena_hard() to look at how many threads are assigned to the
candidate choice, rather than checking whether the arena is
uninitialized.  This bug potentially caused more arenas to be
initialized than necessary.

include/jemalloc/jemalloc_defs.h.in

@@ -68,6 +68,20 @@
  */
 #undef JEMALLOC_MALLOC_THREAD_CLEANUP
 
+/*
+ * Defined if threaded initialization is known to be safe on this platform.
+ * Among other things, it must be possible to initialize a mutex without
+ * triggering allocation in order for threaded allocation to be safe.
+ */
+#undef JEMALLOC_THREADED_INIT
+
+/*
+ * Defined if the pthreads implementation defines
+ * _pthread_mutex_init_calloc_cb(), in which case the function is used in order
+ * to avoid recursive allocation during mutex initialization.
+ */
+#undef JEMALLOC_MUTEX_INIT_CB
+
 /* Defined if __attribute__((...)) syntax is supported. */
 #undef JEMALLOC_HAVE_ATTR
 #ifdef JEMALLOC_HAVE_ATTR