Enable C++ exceptions for the ASIO tests.

Change-Id: I50821fcdc4780f336ad6887623f16e0cfc276387
diff --git a/BUILD.gn b/BUILD.gn
index 5ca22aa..61a1e89 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -628,4 +628,6 @@
   deps = [
     ":asio",
   ]
+
+  configs -= [ "//build/config:no_exceptions" ]
 }