Merge c763cacb88 into merged_master (Bitcoin PR #20938)

build-aux/m4/l_atomic.m4

@@ -14,6 +14,9 @@ m4_define([_CHECK_ATOMIC_testbody], [[
   #include <cstdint>
 
   int main() {
+    std::atomic<bool> lock{true};
+    std::atomic_exchange(&lock, false);
+
     std::atomic<int64_t> a{};
 
     int64_t v = 5;

src/bitcoin-util.cpp

@@ -25,6 +25,7 @@
 #include <util/system.h>
 #include <util/translation.h>
 
+#include <atomic>
 #include <functional>
 #include <memory>
 #include <stdio.h>