Fix:

blackvoltimeextrapolation.cpp:39:50: error: implicit instantiation of undefined template 'std::vector<double>'
            return std::max(varianceSurface(times.back(), strike), 0.0) / times.back() * t;
                                                 ^

https://github.com/lballabio/QuantLib/issues/2557
--- ql/termstructures/volatility/equityfx/blackvoltimeextrapolation.hpp
+++ ql/termstructures/volatility/equityfx/blackvoltimeextrapolation.hpp
@@ -27,6 +27,7 @@
 
 #include <ql/types.hpp>
 #include <functional>
+#include <vector>
 
 namespace QuantLib {