utils: Wrap socket() and pipe() to reduce syscalls

Some platforms provide an implementation of socket() and pipe2() that allow the
caller to specify that the resulting file descriptors should be non-blocking.

Using these allows us to potentially elide 3 calls into 1 by avoiding extraneous
calls to fcntl() to set the O_NONBLOCK flag afterwards.

In passing, change ast_alertpipe_init() to use pipe2() directly instead of the
wrapper if it is available.

Change-Id: I3ebe654fb549587537161506c6c950f4ab298bb0

main/alertpipe.c

@@ -51,6 +51,15 @@ int ast_alertpipe_init(int alert_pipe[2])
 
 #endif
 
+#ifdef HAVE_PIPE2
+
+	if (pipe2(alert_pipe, O_NONBLOCK)) {
+		ast_log(LOG_WARNING, "Failed to create alert pipe: %s\n", strerror(errno));
+		return -1;
+	}
+
+#else
+
 	if (pipe(alert_pipe)) {
 		ast_log(LOG_WARNING, "Failed to create alert pipe: %s\n", strerror(errno));
 		return -1;
@@ -62,6 +71,8 @@ int ast_alertpipe_init(int alert_pipe[2])
 		}
 	}
 
+#endif
+
 	return 0;
 }