[clang] Add an off-by-default warning to complain about MSVC bitfield padding (PR #117428)

[Oliver Hunt via cfe-commits]

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@@ -19213,6 +19213,29 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
 
     if (Record && FD->getType().isVolatileQualified())
       Record->setHasVolatileMember(true);
+    auto IsNonDependentBitField = [](const FieldDecl *FD) {
+      if (!FD->isBitField())
+        return false;
+      if (FD->getType()->isDependentType())
+        return false;
+      return true;
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ojhunt wrote:

I think I did this intentionally as I sometimes feel like explicit true/false returns are clearer, I'm happy with either Aaron or @Sirraide's suggestion but I want to confirm that others don't have my clarity concerns :D

https://github.com/llvm/llvm-project/pull/117428