threading: use a reverse lock rather than manual critsect macros

No functional change.

src/rpc/mining.cpp

@@ -704,7 +704,7 @@ static RPCHelpMan getblocktemplate()
     NodeContext& node = EnsureAnyNodeContext(request.context);
     ChainstateManager& chainman = EnsureChainman(node);
     Mining& miner = EnsureMining(node);
-    LOCK(cs_main);
+    WAIT_LOCK(cs_main, csmain_lock);
     uint256 tip{CHECK_NONFATAL(miner.getTip()).value().hash};
 
     std::string strMode = "template";
@@ -810,8 +810,8 @@ static RPCHelpMan getblocktemplate()
         }
 
         // Release lock while waiting
-        LEAVE_CRITICAL_SECTION(cs_main);
         {
+            REVERSE_LOCK(csmain_lock, cs_main);
             MillisecondsDouble checktxtime{std::chrono::minutes(1)};
             while (IsRPCRunning()) {
                 // If hashWatchedChain is not a real block hash, this will
@@ -830,8 +830,6 @@ static RPCHelpMan getblocktemplate()
                 checktxtime = std::chrono::seconds(10);
             }
         }
-        ENTER_CRITICAL_SECTION(cs_main);
-
         tip = CHECK_NONFATAL(miner.getTip()).value().hash;
 
         if (!IsRPCRunning())