[clang] [llvm] [DirectX] Validate registers are bound to root signature (PR #146785)

[Finn Plummer via cfe-commits]

================
@@ -84,8 +128,150 @@ static void reportOverlappingBinding(Module &M, DXILResourceMap &DRM) {
   }
 }
 
+static void reportRegNotBound(Module &M,
+                              llvm::hlsl::rootsig::RangeInfo Unbound) {
+  SmallString<128> Message;
+  raw_svector_ostream OS(Message);
+  OS << "register " << ResourceClassToString(Unbound.Class)
+     << " (space=" << Unbound.Space << ", register=" << Unbound.LowerBound
+     << ")"
+     << " is not defined in Root Signature";
----------------
inbelic wrote:

```suggestion
     << " does not have a binding in the Root Signature";
```

https://github.com/llvm/llvm-project/pull/146785