Reduce cpp conditional logic complexity.

Convert configuration-related cpp conditional logic to use static
constant variables, e.g.:

  #ifdef JEMALLOC_DEBUG
    [...]
  #endif

becomes:

  if (config_debug) {
    [...]
  }

The advantage is clearer, more concise code.  The main disadvantage is
that data structures no longer have conditionally defined fields, so
they pay the cost of all fields regardless of whether they are used.  In
practice, this is only a minor concern; config_stats will go away in an
upcoming change, and config_prof is the only other major feature that
depends on more than a few special-purpose fields.

include/jemalloc/internal/mutex.h

@@ -3,14 +3,14 @@
 
 #ifdef JEMALLOC_OSSPIN
 typedef OSSpinLock malloc_mutex_t;
+#define	MALLOC_MUTEX_INITIALIZER 0
 #else
 typedef pthread_mutex_t malloc_mutex_t;
-#endif
-
-#ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
-#  define MALLOC_MUTEX_INITIALIZER PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
-#else
-#  define MALLOC_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+#  ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
+#    define MALLOC_MUTEX_INITIALIZER PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
+#  else
+#    define MALLOC_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+#  endif
 #endif
 
 #endif /* JEMALLOC_H_TYPES */