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

tests/Android.mk

@@ -57,11 +57,11 @@ test_c_flags = \
     -fno-builtin \
 
 test_src_files = \
-    debug_format_test.cpp \
     dirent_test.cpp \
     fenv_test.cpp \
     getauxval_test.cpp \
     getcwd_test.cpp \
+    libc_logging_test.cpp \
     libgen_test.cpp \
     math_test.cpp \
     netdb_test.cpp \