Merge bitcoin/bitcoin#32781: refactor: modernize deprecated ipc headers

74b7e9c7db refactor: modernize deprecated ipc headers (Sjors Provoost)

Pull request description:

  Split off from #31802.

  Pre-empt tidy warning when multiprocess is on by default:

  ```
  [10:33:51.654] /ci_container_base/src/ipc/capnp/protocol.cpp:20:10: error: inclusion of deprecated C++ header 'errno.h'; consider using 'cerrno' instead [modernize-deprecated-headers,-warnings-as-errors]
  [10:33:51.654]    20 | #include <errno.h>
  [10:33:51.654]       |          ^~~~~~~~~
  [10:33:51.654]       |          <cerrno>
  [10:33:51.654] 919 warnings generated.
  ```

  https://github.com/bitcoin/bitcoin/pull/31802/checks?check_run_id=43968493627

ACKs for top commit:
  maflcko:
    lgtm ACK 74b7e9c7db
  ryanofsky:
    Code review ACK 74b7e9c7db

Tree-SHA512: a629e9849b420c9de52dc7a74d35ca14c3522784ac101a189b20d3439a4735e2f3bb766864938abb2fc248eb94ec15c71c35db69a3267b6c29ef26e0f91a79ab

src/ipc/capnp/protocol.cpp

@@ -16,8 +16,8 @@
 #include <mp/util.h>
 #include <util/threadnames.h>
 
-#include <assert.h>
-#include <errno.h>
+#include <cassert>
+#include <cerrno>
 #include <future>
 #include <memory>
 #include <mutex>

src/ipc/interfaces.cpp

@@ -15,10 +15,10 @@
 
 #include <cstdio>
 #include <cstdlib>
+#include <cstring>
 #include <functional>
 #include <memory>
 #include <stdexcept>
-#include <string.h>
 #include <string>
 #include <unistd.h>
 #include <utility>

src/ipc/process.cpp

@@ -13,11 +13,11 @@
 
 #include <cstdint>
 #include <cstdlib>
-#include <errno.h>
+#include <cstring>
+#include <cerrno>
 #include <exception>
 #include <iostream>
 #include <stdexcept>
-#include <string.h>
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>