Fix libtcmalloc path on Buster.

etc/default/slapd

@@ -21,6 +21,13 @@ then
     export LD_PRELOAD="/usr/lib/libtcmalloc_minimal.so.4"
 fi
 
+# And the newest version of tcmalloc is the best of all worlds.
+# Use it if is available.
+if [ -e /usr/lib/x86_64-linux-gnu/libtcmalloc_minimal.so.4 ]
+then
+    export LD_PRELOAD="/usr/lib/x86_64-linux-gnu/libtcmalloc_minimal.so.4"
+fi
+
 # Specify a sentinel file that matches current practice
 SLAPD_SENTINEL_FILE=/etc/noldap