Duplicate debug metadata for DIBasicType

[jiel-nv]

The debug metadata cache is not working as expected, look at the following njit reproducer,

$ cat simple.py
from numba import njit

@njit("void(int64)", debug=True)
def f(x):
    y = x
    z = x
$ NUMBA_DUMP_LLVM=1 python simple.py | grep DIBasicType
!2 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i8", size: 8)
!5 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i8", size: 8)
!8 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i32", size: 32)
!10 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i8", size: 8)
!13 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i8", size: 8)
!16 = !DIBasicType(encoding: DW_ATE_unsigned, name: "i32", size: 32)
!22 = !DIBasicType(encoding: DW_ATE_signed, name: "int64", size: 64)
!28 = !DIBasicType(encoding: DW_ATE_signed, name: "int64", size: 64)
!32 = !DIBasicType(encoding: DW_ATE_signed, name: "int64", size: 64)
!35 = !DIBasicType(encoding: DW_ATE_signed, name: "int64", size: 64)

For the same DWARF encoding and name,, e.g. {DW_ATE_signed, "int64"}, the corresponding DIBasicType are created multiple times.

[jiel-nv]

The problem is in llvmlite, where module.py has function add_debug_info() designed with using '_metadatacache' to deduplicate the metadata DIValue, however, the 'key' tuple contains 'encoding' with value to be an address / pointer to a DIToken object,

(Pdb) c
> /home/jiel/miniconda3/envs/numba-dev1/lib/python3.10/site-packages/llvmlite/ir/module.py(79)add_debug_info()
-> if key not in self._metadatacache:
(Pdb) p key
('DIBasicType', (('encoding', <llvmlite.ir.values.DIToken object at 0x7ff3bac3f6d0>), ('name', 'int64'), ('size', 64)), False)

The same encoding value, e.g. 'DW_ATE_signed', coule have multiple instance of DIToken when object initiated via
'encoding': ir.DIToken(ditok),

I'm working on a fix.