idb2pat.py issue on IDA 7.5

[KulaGGin]

If you run idb2pat.py on IDA version 7.5, you'll get this error:

 error: Traceback (most recent call last):
  File "<string>", line 478, in <module>
  File "<string>", line 455, in main
  File "<string>", line 416, in get_pat_file
NameError: global name 'askfile_c' is not defined

Which is caused by newer version of IDA and renaming of the askfile_c member to ask_file in the ida_kernwin type, as explained in this porting guide by hex-rays.

There are many more errors like this one for many members in different types.

One possible solution I see is to have 2 versions of the file now: idb2pat.py and idb2pat_74plus.py for appropriate IDA version.

After updating the file and changing names for all the members(which changed names), I was able to succesfully generate .sig file for a simple test Hello World VC++ solution for Windows from a version with .pdb loaded for the same executable without the .pdb loaded:

#include <iostream>

void PrintHelloWorld()
{
    std::cout << "Hello World!\n";
}

int main()
{
    PrintHelloWorld();
}

[mr-tz]

I think idaapi.ask_file works in all versions and we can just replace this API call.
Alternatively, we could check the IDA version and pick the appropriate API.