MPI include guard

Author: franzpoeschel

examples/10_streaming_write.cpp

@@ -1,11 +1,14 @@
-#include <mpi.h>
 #include <openPMD/openPMD.hpp>
 
 #include <algorithm>
 #include <iostream>
 #include <memory>
 #include <numeric> // std::iota
 
+#if openPMD_HAVE_MPI
+#include <mpi.h>
+#endif
+
 using std::cout;
 using namespace openPMD;