[clang] [Serialization] Use specialized decl hash function for GlobalDeclID (PR #95730)

[Ilya Biryukov via cfe-commits]

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@@ -230,7 +230,11 @@ template <> struct DenseMapInfo<clang::GlobalDeclID> {
   }
 
   static unsigned getHashValue(const GlobalDeclID &Key) {
-    return DenseMapInfo<DeclID>::getHashValue(Key.get());
+    // Our default hash algorithm for 64 bits integer may not be very good.
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ilya-biryukov wrote:

NIT: could you add a FIXME to remove this after we update the hash functions?

https://github.com/llvm/llvm-project/pull/95730