[llvm] [DebugInfo] Emit negative DW_AT_bit_offset in explicit signed form (PR #87994)

[David Blaikie via llvm-commits]

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@@ -1664,7 +1666,12 @@ DIE &DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
         if (Asm->getDataLayout().isLittleEndian())
           Offset = FieldSize - (Offset + Size);
 
-        addUInt(MemberDie, dwarf::DW_AT_bit_offset, std::nullopt, Offset);
+        if (Offset < 0)
+          addSInt(MemberDie, dwarf::DW_AT_bit_offset, dwarf::DW_FORM_sdata,
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dwblaikie wrote:

Does this need a version check to make sure it's used in DWARFv3, but not earlier? (or perhaps we don't support DWARFv2? Not sure - but the `useDWARF2Bitfields` above gives me pause)

https://github.com/llvm/llvm-project/pull/87994