[clang-cpp] Overloads in vtable building lead to assertion error.

[intrigus-lgtm]

Running this code

struct c
{
  virtual int d();
  virtual int d(int);
};

results in:

esbmc: esbmc/src/clang-cpp-frontend/clang_cpp_convert_vft.cpp:585: void clang_cpp_convertert::add_vtable_variable_symbols(const clang::CXXRecordDecl&, const struct_typet&, const switch_table&): Assertion `value.type() == compo.type()' failed.

The reason pretty much is that the current code does not handle overloads.
method_name is just d in both cases.

esbmc/src/clang-cpp-frontend/clang_cpp_convert_vft.cpp

Line 108 in fb01095

comp.type().set("#virtual_name", method_name);

esbmc/src/clang-cpp-frontend/clang_cpp_convert_vft.cpp

Line 110 in fb01095

comp.set("virtual_name", method_name);

(I don't know which of the two lines is the exact culprit but it doesn't really matter)

The end result is that there is only one entry for d in the switch_map here and so we are guaranteed to find a wrong type:

esbmc/src/clang-cpp-frontend/clang_cpp_convert_vft.cpp

Line 582 in fb01095

switch_map.find(compo.get("virtual_name").as_string());