liblog: suppress pmsg on user builds

(cherry pick from commit 7ef5249afacffe3901e3a602372c7d34cf655675)

- 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.mk b/liblog/Android.mk
index 01c8e77..b24b489 100644
--- a/liblog/Android.mk
+++ b/liblog/Android.mk
@@ -23,6 +23,7 @@
 #       $(LOCAL_PATH)/event.logtags)
 # so make sure we do not regret hard-coding it as follows:
 liblog_cflags := -DLIBLOG_LOG_TAG=1005
+liblog_cflags += -DSNET_EVENT_LOG_TAG=1397638484
 
 liblog_sources := log_event_list.c log_event_write.c logger_write.c
 liblog_sources += config_write.c logger_name.c logger_lock.c