[lldb][test] Skip bitfield enum tests for DWARF v2 and below

Clang's v2 output appears to be missing a key DW_AT_type attribute,
and this causes the "max" of the unsigned enum to appear as -1 instead
of "max" aka 3.

```
(BitfieldStruct) $0 = {
  signed_min = min
  signed_other = -1
  signed_max = max
  unsigned_min = min
  unsigned_other = 1
  unsigned_max = -1
}
```

Test added by #96202.

Author: DavidSpickett

lldb/test/API/commands/expression/bitfield_enums/TestBitfieldEnums.py

@@ -10,6 +10,9 @@
 
 
 class TestBitfieldEnum(TestBase):
+    # clang's DWARF v2 output is missing DW_AT_type which causes unsigned_max to
+    # appear as -1 instead of the "max" enumerator, whose value is 3.
+    @skipIf(dwarf_version=["<", "3"], compiler="clang")
     def test_bitfield_enums(self):
         self.build()