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/huge.h

@@ -9,12 +9,10 @@
 /******************************************************************************/
 #ifdef JEMALLOC_H_EXTERNS
 
-#ifdef JEMALLOC_STATS
 /* Huge allocation statistics. */
 extern uint64_t		huge_nmalloc;
 extern uint64_t		huge_ndalloc;
 extern size_t		huge_allocated;
-#endif
 
 /* Protects chunk-related data structures. */
 extern malloc_mutex_t	huge_mtx;
@@ -27,10 +25,8 @@ void	*huge_ralloc(void *ptr, size_t oldsize, size_t size, size_t extra,
     size_t alignment, bool zero);
 void	huge_dalloc(void *ptr, bool unmap);
 size_t	huge_salloc(const void *ptr);
-#ifdef JEMALLOC_PROF
 prof_ctx_t	*huge_prof_ctx_get(const void *ptr);
 void	huge_prof_ctx_set(const void *ptr, prof_ctx_t *ctx);
-#endif
 bool	huge_boot(void);
 
 #endif /* JEMALLOC_H_EXTERNS */