Implement Runtime::Abort and switch LOG(FATAL) over to it.

Runtime::Abort takes arguments so it can provide less misleading log output,
but this shouldn't matter to callers because they should be using LOG(FATAL)
anyway.

This patch also fixes an errno/errno_ mixup in the logging code.

Change-Id: If24b66b7bbf0bf7c0ecb93dd806d82b1d21ee239
diff --git a/src/logging.h b/src/logging.h
index 24ffdbc..98eb953 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -109,6 +109,8 @@
 
  private:
   std::stringstream buffer_;
+  const char* file_;
+  int line_;
   LogSeverity severity_;
   int errno_;