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/arch-arm/bionic/atexit_legacy.c b/libc/arch-arm/bionic/atexit_legacy.c
index 6e299ac..f35c68d 100644
--- a/libc/arch-arm/bionic/atexit_legacy.c
+++ b/libc/arch-arm/bionic/atexit_legacy.c
@@ -27,7 +27,7 @@
  */
 
 #include <sys/types.h>
-#include <private/logd.h>
+#include <private/libc_logging.h>
 #include <stdio.h>
 
 /*
@@ -52,7 +52,7 @@
      */
     static char const warning[] = "WARNING: generic atexit() called from legacy shared library\n";
 
-    __libc_android_log_write(ANDROID_LOG_WARN, "libc", warning);
+    __libc_format_log(ANDROID_LOG_WARN, "libc", warning);
     fprintf(stderr, warning);
 
     return (__cxa_atexit((void (*)(void *))func, NULL, NULL));