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
diff --git a/libc/bionic/openat.c b/libc/bionic/openat.c
index c1abbaa..2d09d17 100644
--- a/libc/bionic/openat.c
+++ b/libc/bionic/openat.c
@@ -29,7 +29,7 @@
 #include <fcntl.h>
 #include <stdarg.h>
 #include <stdlib.h>
-#include <private/logd.h>
+#include "libc_logging.h"
 
 extern int  __openat(int, const char*, int, int);
 
@@ -61,4 +61,3 @@
 
     return __openat(fd, pathname, flags, 0);
 }
-