init: only use pipe2 if availabile, check in configure

configure.ac

@@ -925,6 +925,8 @@ AC_CHECK_DECLS([strnlen])
 dnl Check for daemon(3), unrelated to --with-daemon (although used by it)
 AC_CHECK_DECLS([daemon])
 
+AC_CHECK_DECLS([pipe2])
+
 AC_CHECK_DECLS([le16toh, le32toh, le64toh, htole16, htole32, htole64, be16toh, be32toh, be64toh, htobe16, htobe32, htobe64],,,
 		[#if HAVE_ENDIAN_H
                  #include <endian.h>

src/shutdown.cpp

@@ -32,7 +32,7 @@ static int g_shutdown_pipe[2] = {-1, -1};
 bool InitShutdownState()
 {
 #ifndef WIN32
-#if HAVE_O_CLOEXEC
+#if HAVE_O_CLOEXEC && HAVE_DECL_PIPE2
     // If we can, make sure that the file descriptors are closed on exec()
     // to prevent interference.
     if (pipe2(g_shutdown_pipe, O_CLOEXEC) != 0) {