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/linker/linker_debug.h b/linker/linker_debug.h
index 8fc235f..7d24853 100644
--- a/linker/linker_debug.h
+++ b/linker/linker_debug.h
@@ -58,7 +58,7 @@
 
 /*********************************************************************/
 
-#include <private/debug_format.h>
+#include "private/libc_logging.h"
 
 __LIBC_HIDDEN__ extern int gLdDebugVerbosity;