Support ANDROID_LOG_TAGS.

This is the dalvik-compatible solution to the "I don't want non-FATAL logging
in my test output" problem.

Change-Id: I51b7b883ce89604af4661696e7c7b041a0ef8211
diff --git a/src/logging_linux.cc b/src/logging_linux.cc
index 4e7c796..84a6843 100644
--- a/src/logging_linux.cc
+++ b/src/logging_linux.cc
@@ -34,11 +34,10 @@
 }
 
 void LogMessage::LogLine(const char* message) {
-  std::ostream &out =
-      (gLogVerbosity.logging_stream == NULL ? std::cerr : *gLogVerbosity.logging_stream);
-  out << "VDIWEFF"[data_->severity] << ' '
-      << StringPrintf("%5d %5d", getpid(), ::art::GetTid()) << ' '
-      << data_->file << ':' << data_->line_number << "] " << message << std::endl;
+  std::ostream& os(std::cerr);
+  os << "VDIWEFF"[data_->severity] << ' '
+     << StringPrintf("%5d %5d", getpid(), ::art::GetTid()) << ' '
+     << data_->file << ':' << data_->line_number << "] " << message << std::endl;
 }
 
 }  // namespace art