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/ctl.h

@@ -32,7 +32,6 @@ struct ctl_arena_stats_s {
 	unsigned		nthreads;
 	size_t			pactive;
 	size_t			pdirty;
-#ifdef JEMALLOC_STATS
 	arena_stats_t		astats;
 
 	/* Aggregate stats for small size classes, based on bin stats. */
@@ -43,11 +42,9 @@ struct ctl_arena_stats_s {
 
 	malloc_bin_stats_t	*bstats;	/* nbins elements. */
 	malloc_large_stats_t	*lstats;	/* nlclasses elements. */
-#endif
 };
 
 struct ctl_stats_s {
-#ifdef JEMALLOC_STATS
 	size_t			allocated;
 	size_t			active;
 	size_t			mapped;
@@ -61,11 +58,8 @@ struct ctl_stats_s {
 		uint64_t	nmalloc;	/* huge_nmalloc */
 		uint64_t	ndalloc;	/* huge_ndalloc */
 	} huge;
-#endif
 	ctl_arena_stats_t	*arenas;	/* (narenas + 1) elements. */
-#ifdef JEMALLOC_SWAP
 	size_t			swap_avail;
-#endif
 };
 
 #endif /* JEMALLOC_H_STRUCTS */