malloc: Increase tcache fill count from 16 to 32

This avoids a regression in the omnetpp and xalancbmk benchmarks
of SPEC.  Apparently, these benchmarks are very sensitive to the
fill rate in malloc.

Suggested-by: Wilco Dijkstra <wilco.dijkstra@arm.com>
Tested-by: Wilco Dijkstra <wilco.dijkstra@arm.com>

malloc/malloc.c

@@ -306,7 +306,7 @@ verify (PTRDIFF_MAX <= SIZE_MAX / 2);
 
 /* This is another arbitrary limit, which tunables can change.  Each
    tcache bin will hold at most this number of chunks.  */
-# define TCACHE_FILL_COUNT 16
+# define TCACHE_FILL_COUNT 32
 
 /* Maximum chunks in tcache bins for tunables.  This value must fit the range
    of tcache->num_slots[] entries, else they may overflow.  */