DLL support missing on Windows

[tim-lebedkov]

If an address is not in the current executable, but in an external DLL not compiled with GCC (e.g. KERNEL.DLL), the callback is called with a NULL file name, NULL function name and 0 for line number. At least the filename could be determined as "KERNEL.DLL". Using function exports table it is also possible to find out the function name.

Platform: Windows, MinGW-w64, ucrt64.