Remove --disable-tcache.

Simplify configuration by removing the --disable-tcache option, but
replace the testing for that configuration with
--with-malloc-conf=tcache:false.

Fix the thread.arena and thread.tcache.flush mallctls to work correctly
if tcache is disabled.

This partially resolves #580.

include/jemalloc/internal/tcache_structs.h

@@ -40,23 +40,14 @@ struct tcache_s {
 	 * element of tbins is initialized to point to the proper offset within
 	 * this array.
 	 */
-#ifdef JEMALLOC_TCACHE
 	tcache_bin_t	tbins_small[NBINS];
-#else
-	tcache_bin_t	tbins_small[0];
-#endif
 	/* Data accessed less often below. */
 	ql_elm(tcache_t) link;		/* Used for aggregating stats. */
 	arena_t		*arena;		/* Associated arena. */
 	szind_t		next_gc_bin;	/* Next bin to GC. */
-#ifdef JEMALLOC_TCACHE
 	/* For small bins, fill (ncached_max >> lg_fill_div). */
 	uint8_t		lg_fill_div[NBINS];
 	tcache_bin_t	tbins_large[NSIZES-NBINS];
-#else
-	uint8_t		lg_fill_div[0];
-	tcache_bin_t	tbins_large[0];
-#endif
 };
 
 /* Linkage for list of available (previously used) explicit tcache IDs. */