Clean up internal libc logging.

We only need one logging API, and I prefer the one that does no
allocation and is thus safe to use in any context.

Also use O_CLOEXEC when opening the /dev/log files.

Move everything logging-related into one header file.

Change-Id: Ic1e3ea8e9b910dc29df351bff6c0aa4db26fbb58

libc/bionic/assert.cpp

@@ -32,8 +32,7 @@
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <private/debug_format.h>
-#include <private/logd.h>
+#include "libc_logging.h"
 
 // We log to stderr for the benefit of "adb shell" users, and the log for the benefit
 // of regular app developers who want to see their asserts.