util: Replace non-threadsafe strerror

Some uses of non-threadsafe `strerror` have snuck into the code since
they were removed in #4152. Add a wrapper `SysErrorString` for
thread-safe strerror alternatives and replace all uses of `strerror`
with this.

src/bitcoind.cpp

@@ -20,6 +20,7 @@
 #include <util/check.h>
 #include <util/strencodings.h>
 #include <util/syscall_sandbox.h>
+#include <util/syserror.h>
 #include <util/system.h>
 #include <util/threadnames.h>
 #include <util/tokenpipe.h>
@@ -206,7 +207,7 @@ static bool AppInit(NodeContext& node, int argc, char* argv[])
                 }
                 break;
             case -1: // Error happened.
-                return InitError(Untranslated(strprintf("fork_daemon() failed: %s\n", strerror(errno))));
+                return InitError(Untranslated(strprintf("fork_daemon() failed: %s\n", SysErrorString(errno))));
             default: { // Parent: wait and exit.
                 int token = daemon_ep.TokenRead();
                 if (token) { // Success