Fix GCC debug build.

Change-Id: I11a3eb40a1b5f609e69d42acd32e56c9c1a8f473
diff --git a/gn/standalone/BUILD.gn b/gn/standalone/BUILD.gn
index 01fcafb..d0b8a20 100644
--- a/gn/standalone/BUILD.gn
+++ b/gn/standalone/BUILD.gn
@@ -108,6 +108,10 @@
     libs += [ "log" ]
   }
 
+  if (is_debug) {
+    libs += [ "dl" ]
+  }
+
   if (is_android) {
     asmflags += [ "--target=$android_abi_target" ]
     cflags += [