liblog: suppress pmsg on user builds

- add optimized & cached LIBLOG_HIDDEN __android_log_is_debuggable()
- check when writing, either LOG_ID_SECURITY, SafetyNet or
  debuggable when pushing content to the pmsg buffer.

Bug: 27566046
Change-Id: I85f1b55ec329b38e00f4183836b6ed53046c323d
diff --git a/liblog/Android.bp b/liblog/Android.bp
index 59c696b..302e63c 100644
--- a/liblog/Android.bp
+++ b/liblog/Android.bp
@@ -83,6 +83,7 @@
         //       $(LOCAL_PATH)/event.logtags)
         // so make sure we do not regret hard-coding it as follows:
         "-DLIBLOG_LOG_TAG=1005",
+        "-DSNET_EVENT_LOG_TAG=1397638484",
     ],
     compile_multilib: "both",
     stl: "none",