fix clang builds by including <string> where needed

diff --git a/src/kernel/EngineImpl.hpp b/src/kernel/EngineImpl.hpp
index d038e3b..d3501dc 100644 (file)
--- a/src/kernel/EngineImpl.hpp
+++ b/src/kernel/EngineImpl.hpp
@@ -6,6 +6,7 @@
 #include <simgrid/s4u/forward.hpp>
 #include <xbt/dict.h>
 
+#include <string>
 #include <unordered_map>
 
 namespace simgrid {