#185735 added the `vbases.test`, which compiles with
`--target=x86_64-windows-msvc`. This will cause the final executable to
be linked to `libcmt.lib`. That doesn't work on ARM, so this PR changes
the command line to link without the default libraries. They're not
needed if we disable `/GS` (buffer security check) like in other tests.
We use `%clang_cl` over `%build` to be able to compile with DWARF as
well.
When a class indirectly inherits from a class with virtual bases, it
will get an `LF_IVBCLASS` record in its fieldlist, even though it
doesn't directly inherit that class.
In the following example, `UserUser` inherits from `User`, which
virtually inherits from `VBase`:
```cpp
struct User : public virtual VBase {};
struct UserUser : public User {};
```
For this we get
```
0x1015 | LF_FIELDLIST [size = 72]
- LF_BCLASS
type = 0x1002 (-> 0x102A), offset = 0, attrs = public
- LF_IVBCLASS
base = 0x1003, vbptr = 0x1005, vbptr offset = 0, vtable index = 1
attrs = public (...)
0x1016 | LF_STRUCTURE [size = 48] `UserUser`
unique name: `.?AUUserUser@@`
vtable: <no type>, base list: <no type>, field list: 0x1015
options: has ctor / dtor | has unique name | overloaded operator | overloaded operator=, sizeof 16
0x1029 | LF_FIELDLIST [size = 56]
- LF_VBCLASS
base = 0x1003, vbptr = 0x1005, vbptr offset = 0, vtable index = 1
attrs = public (...)
0x102A | LF_STRUCTURE [size = 40] `User`
unique name: `.?AUUser@@`
vtable: <no type>, base list: <no type>, field list: 0x1029
options: has ctor / dtor | has unique name | overloaded operator | overloaded operator=, sizeof 16
```
If I understand correctly, then `LF_IVBCLASS` indicates that if this
class (e.g. `UserUser`) is created as the most derived object, it will
host the class (e.g. `VBase`).
The VS debugger actually shows this as a separate field. LLDB on the
other hand doesn't, so I removed it.
---------
Co-authored-by: Zequan Wu <zequanwu@google.com>
