Tag types like stucts or enums didn't have a declaration attached to
them. The source locations are present in the IPI stream in
`LF_UDT_MOD_SRC_LINE` records:
```
0x101F | LF_UDT_MOD_SRC_LINE [size = 18, hash = 0x1C63]
udt = 0x1058, mod = 3, file = 1, line = 0
0x2789 | LF_UDT_MOD_SRC_LINE [size = 18, hash = 0x1E5A]
udt = 0x1253, mod = 35, file = 93, line = 17069
```
The file is an ID in the string table `/names`:
```
ID | String
1 | '\<unknown>'
12 | 'D:\a\_work\1\s\src\ExternalAPIs\WindowsSDKInc\c\Include\10.0.22621.0\um\wingdi.h'
93 | 'D:\a\_work\1\s\src\ExternalAPIs\WindowsSDKInc\c\Include\10.0.22621.0\um\winnt.h'
```
Here, we're not interested in `mod`. This would indicate which module
contributed the UDT.
I was looking at Rustc's PDB and found that it uses `<unknown>` for some
types, so I added a check for that.
This makes two DIA PDB shell tests to work with the native PDB plugin.
---------
Co-authored-by: Michael Buch <michaelbuch12@gmail.com>
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