[compiler-rt] Print out which symbolizer are we using when verbosity >= 2

[kubamracek]

Summary

Just adding a few VReport()'s to print the name and path (for external symbolizers) of the symbolizer in use.

[samsonov]

LGTM

[kubamracek]

Committed r231428.

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

private:
   BlockingMutex mu_;
 
   typedef IntrusiveList<SymbolizerTool>::Iterator Iterator;
   IntrusiveList<SymbolizerTool> tools_;
 };
 
 static SymbolizerTool *ChooseSymbolizer(LowLevelAllocator *allocator) {
   if (!common_flags()->symbolize) {
+    VReport(2, "Symbolizer is disabled.\n");
     return nullptr;
   }
   if (SymbolizerTool *tool = InternalSymbolizer::get(allocator)) {
+    VReport(2, "Using internal symbolizer.\n");
     return tool;
   }
   if (SymbolizerTool *tool = LibbacktraceSymbolizer::get(allocator)) {
+    VReport(2, "Using libbacktrace symbolizer.\n");
     return tool;
   }
   const char *path_to_external = common_flags()->external_symbolizer_path;
   if (path_to_external && path_to_external[0] == '\0') {
     // External symbolizer is explicitly disabled. Do nothing.
     return nullptr;
   }
   // Find path to llvm-symbolizer if it's not provided.
   if (!path_to_external) {
     path_to_external = FindPathToBinary("llvm-symbolizer");
   }
   if (path_to_external) {
+    VReport(2, "Using llvm-symbolizer at path: %s\n", path_to_external);
     return new(*allocator) LLVMSymbolizer(path_to_external, allocator);
   }
   if (common_flags()->allow_addr2line) {
     // If llvm-symbolizer is not found, try to use addr2line.
     if (const char *addr2line_path = FindPathToBinary("addr2line")) {
+      VReport(2, "Using addr2line at path: %s\n", addr2line_path);
       return new(*allocator) Addr2LinePool(addr2line_path, allocator);
     }
   }
+  VReport(2, "No internal or external symbolizer found.\n");
   return nullptr;
 }
 
 Symbolizer *Symbolizer::PlatformInit() {
   IntrusiveList<SymbolizerTool> list;
   list.clear();
   if (SymbolizerTool *tool = ChooseSymbolizer(&symbolizer_allocator_)) {
     list.push_back(tool);
   }
   return new(symbolizer_allocator_) POSIXSymbolizer(list);
 }
 
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_POSIX