Directly calling callback functions causes a crash

[ahueck]

A crash during the compilation is caused by explicit/direct calls to the various callback functions:

#include <stddef.h>
void __typeart_leave_scope(int alloca_count);
int main(void) {
  __typeart_leave_scope(0);
  return 0;
}

Potential fix

In TypeARTFunctions.cpp, check if the function is already declared in the module.

Rough fix outline

TAFunctionDeclarator::make_function(...)  {
  ...
  const auto do_make = [&](auto& name, auto f_type) {
    const bool has_f = m.getFunction(name) != nullptr;
    auto fc          = m.getOrInsertFunction(name, f_type);
    if (has_f) {
      auto fcc = fc.getCallee();
      return dyn_cast<Function>(fc.getCallee()->stripPointerCasts());
    }
    ...