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/string/strchr.c b/libc/string/strchr.c
index 564ea80..93cb250 100644
--- a/libc/string/strchr.c
+++ b/libc/string/strchr.c
@@ -29,7 +29,7 @@
  */
 
 #include <string.h>
-#include <private/logd.h>
+#include "libc_logging.h"
 
 char *
 __strchr_chk(const char *p, int ch, size_t s_len)
diff --git a/libc/string/strrchr.c b/libc/string/strrchr.c
index 5d0415e..14f29c5 100644
--- a/libc/string/strrchr.c
+++ b/libc/string/strrchr.c
@@ -29,7 +29,7 @@
  */
 
 #include <string.h>
-#include <private/logd.h>
+#include "libc_logging.h"
 
 char *
 __strrchr_chk(const char *p, int ch, size_t s_len)