Add includes for missing standard headers

We use symbols from each of these and were relying on them being
included by other headers.

src/backend/distributed/planner/multi_planner.c

@@ -9,6 +9,7 @@
 
 #include "postgres.h"
 
+#include <float.h>
 #include <limits.h>
 
 #include "catalog/pg_type.h"

src/backend/distributed/worker/worker_partition_protocol.c

@@ -20,6 +20,7 @@
 #include <arpa/inet.h>
 #include <netinet/in.h>
 #include <sys/stat.h>
+#include <math.h>
 #include <unistd.h>
 
 #include "access/hash.h"