[clang] [serialization] no transitive decl change (PR #92083)

[Jan Svoboda via cfe-commits]

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@@ -124,6 +130,15 @@ class DeclIDBase {
 
   bool isInvalid() const { return ID == PREDEF_DECL_NULL_ID; }
 
+  unsigned getModuleFileIndex() const { return ID >> 32; }
+
+  unsigned getLocalDeclIndex() const {
+    // Implement it directly instead of calling `llvm::maskTrailingOnes` since
+    // we don't want `MathExtras.h` to be inclued here.
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jansvoboda11 wrote:

Why not? Just to keep the amount of code lower? Can't we move the function body to an implementation file?

https://github.com/llvm/llvm-project/pull/92083