ipc, refactor: Update mp::g_thread_context references

Use new CurrentThread function to be compatible with windows mingw bug
workaround https://github.com/bitcoin-core/libmultiprocess/pull/318

src/ipc/capnp/protocol.cpp

@@ -94,7 +94,7 @@ public:
     void serve(interfaces::Init& init, const std::function<mp::Stream()>& make_stream) override
     {
         assert(!m_loop);
-        mp::g_thread_context.thread_name = mp::ThreadName(m_exe_name);
+        mp::CurrentThread().thread_name = mp::ThreadName(m_exe_name);
         mp::LogOptions opts = {
             .log_fn = IpcLogFn,
             .log_level = GetRequestedIPCLogLevel()

src/ipc/test/fuzz/ipc.cpp

@@ -5,6 +5,7 @@
 #include <primitives/transaction.h>
 #include <capnp/capability.h>
 #include <capnp/rpc.h>
+#include <ipc/util.h>
 #include <kj/memory.h>
 #include <mp/proxy-io.h>
 #include <mp/proxy.h>
@@ -78,10 +79,10 @@ static void initialize_ipc()
     static const auto testing_setup = MakeNoLogFileContext<>();
     (void)testing_setup;
 
-    // Ensure g_thread_context is destroyed after the IPC setup, since C++
-    // destroys thread_local objects in reverse construction order.
-    mp::ThreadContext& thread_context{mp::g_thread_context};
-    (void)thread_context;
+    // Ensure the thread's ThreadContext is created before the IPC setup, so
+    // it is destroyed after it, since C++ destroys thread_local objects in
+    // reverse construction order.
+    mp::CurrentThread();
 
     thread_local static IpcFuzzSetup ipc; // NOLINT(bitcoin-nontrivial-threadlocal)
     g_ipc = &ipc;

src/ipc/util.h

@@ -12,6 +12,7 @@
 #include <cstdint>
 #include <functional>
 #include <kj/debug.h>
+#include <mp/proxy-io.h>
 #include <mp/util.h>
 #include <mp/version.h>
 #include <sys/socket.h>
@@ -52,6 +53,11 @@ inline SocketId StartSpawned(const std::string& connect_info)
     if (!socket) throw std::invalid_argument(strprintf("Invalid socket descriptor '%s'", connect_info));
     return *socket;
 }
+
+inline ThreadContext& CurrentThread()
+{
+    return g_thread_context;
+}
 #endif
 } // namespace mp