Pointer to bind(c) struct does not work in CPython

[certik]

For example in: https://github.com/lcompilers/lpython/pull/2133/files#diff-72df88224d1b2b9b8ec209f998b9bc6411274c70025c78e287347bca0a4847f6R25.

Here is a minimal example:

from lpython import (i32, f32, dataclass, CPtr, Pointer, c_p_pointer, pointer,
        ccallable, empty_c_void_p, f64, ccall, sizeof, i64)

@ccallable
@dataclass
class A:
    x: i32
    y: f32

def f() -> None:
    x: i32
    y: f32
    a1: A = A(3, f32(3.25))
    a2: Pointer[A]
    a2 = pointer(a1)
    print(a2, pointer(a1))
    x = a2.x
    y = a2.y
    assert x == 3
    assert f64(y) == 3.25

f()

This works with LPython, but fails in CPython with:

$ PYTHONPATH=src/runtime/lpython python integration_tests/structs_02b.py 
c_void_p(4346287752) c_void_p(4346287752)
Traceback (most recent call last):
  File "/Users/ondrej/repos/lpython/integration_tests/structs_02b.py", line 22, in <module>
    f()
  File "/Users/ondrej/repos/lpython/integration_tests/structs_02b.py", line 17, in f
    x = a2.x
AttributeError: 'c_void_p' object has no attribute 'x'

The fix there is:

--- a/src/runtime/lpython/lpython.py
+++ b/src/runtime/lpython/lpython.py
@@ -670,10 +670,7 @@ def pointer(x, type_=None):
             return ctypes.cast(ctypes.pointer(ctypes.c_double(x)),
                     ctypes.c_void_p)
         elif is_dataclass(type_):
-            if issubclass(type_, ctypes.Structure):
-                return ctypes.cast(ctypes.pointer(x), ctypes.c_void_p)
-            else:
-                return x
+            return x
         else:
             raise Exception("Type not supported in pointer()")
 

But this makes many other tests fail, things start to fall apart, so this requires further investigation.