Define _LOG as a weak symbol.

So _LOG could be overridden by customized logging
implementations in non-Android systems.

Bug: 35919515
Test: Test on device
Change-Id: I0885c15353c0b1bf66f6f156e7f502f326b85d57
diff --git a/debuggerd/libdebuggerd/utility.cpp b/debuggerd/libdebuggerd/utility.cpp
index 57209aa..744cd72 100644
--- a/debuggerd/libdebuggerd/utility.cpp
+++ b/debuggerd/libdebuggerd/utility.cpp
@@ -41,6 +41,7 @@
   return false;
 }
 
+__attribute__((__weak__, visibility("default")))
 void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
   bool write_to_tombstone = (log->tfd != -1);
   bool write_to_logcat = is_allowed_in_logcat(ltype)