Converting lambdas to std::function in cling

[SylvainCorlay]

The following code is valid and compiles properly in cling, but not in the xeus-cling kernel, which crashes.

#include <functional>

std::function<void()> f = [](){};

In general, we have issues with converting lambdas to std::function when running in the C++ notebook, where the same code compiles fine with normal compilers.

[SylvainCorlay]

cc @vgvassilev who may know what is going on here.

[SylvainCorlay]

I suspect it comes from how we call the metaprocessor, to which we pass a Value unlike the usual cling user interface, and this function probably triggers a bug in that case.