[clang] [Clang][attr] Add 'cfi_salt' attribute (PR #141846)

[Bill Wendling via cfe-commits]

================
@@ -7941,6 +7942,32 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
     return true;
   }
 
+  if (attr.getKind() == ParsedAttr::AT_CFISalt) {
+    if (attr.getNumArgs() == 0)
+      return true;
+
+    // Delay if this is not a function type.
+    StringRef Argument;
+    if (!S.checkStringLiteralArgumentAttr(attr, 0, Argument))
+      return false;
+
+    // Delay if this is not a function type.
+    if (!unwrapped.isFunctionType())
+      return false;
+
+    const auto *FnTy = unwrapped.get()->getAs<FunctionProtoType>();
+    if (!FnTy)
----------------
bwendling wrote:

The attribute is accessible only via the `FunctionProtoType`. To be more accurate, it really needs to be on `extern` function forward decls and the definition, because otherwise the attribute won't propagate correctly.

I'll add a test case to ensure this.

https://github.com/llvm/llvm-project/pull/141846