validation: use stronger EXCLUSIVE_LOCKS_REQUIRED()

bitcoin#24103 added annotations to
denote that the callers of `CChainState::ActivateBestChain()` and
`CChainState::InvalidateBlock()` must not own `m_chainstate_mutex` at
the time of the call.

Replace the added `LOCKS_EXCLUDED()` with a stronger
`EXCLUSIVE_LOCKS_REQUIRED()`, see
https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#negative for the
difference between both.

src/validation.h

@@ -599,7 +599,8 @@ class CChainState
         EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     /** Import blocks from an external file */
-    void LoadExternalBlockFile(FILE* fileIn, FlatFilePos* dbp = nullptr);
+    void LoadExternalBlockFile(FILE* fileIn, FlatFilePos* dbp = nullptr)
+        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex);
 
     /**
      * Update the on-disk chain state.
@@ -641,7 +642,9 @@ class CChainState
      */
     bool ActivateBestChain(
         BlockValidationState& state,
-        std::shared_ptr<const CBlock> pblock = nullptr) LOCKS_EXCLUDED(m_chainstate_mutex, cs_main);
+        std::shared_ptr<const CBlock> pblock = nullptr)
+        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
+        LOCKS_EXCLUDED(::cs_main);
 
     bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
@@ -659,9 +662,15 @@ class CChainState
      *
      * May not be called in a validationinterface callback.
      */
-    bool PreciousBlock(BlockValidationState& state, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
+    bool PreciousBlock(BlockValidationState& state, CBlockIndex* pindex)
+        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
+        LOCKS_EXCLUDED(::cs_main);
+
     /** Mark a block as invalid. */
-    bool InvalidateBlock(BlockValidationState& state, CBlockIndex* pindex) LOCKS_EXCLUDED(m_chainstate_mutex, cs_main);
+    bool InvalidateBlock(BlockValidationState& state, CBlockIndex* pindex)
+        EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
+        LOCKS_EXCLUDED(::cs_main);
+
     /** Remove invalidity status from a block and its descendants. */
     void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);