Fixes:

src/cpp/flann/mpi/flann_mpi_client.cpp:21:5: error: ‘gettimeofday’ was not declared in this scope
   21 |     gettimeofday(&start_time_,NULL);
      |     ^~~~~~~~~~~~

--- a/src/cpp/flann/mpi/flann_mpi_client.cpp
+++ b/src/cpp/flann/mpi/flann_mpi_client.cpp
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <time.h>
+#include <sys/time.h>
 
 #include <cstdlib>
 #include <iostream>