Add -lstdc++ flag for compiling under gcov
diff --git a/grpc.gyp b/grpc.gyp
index 48fb2ba..6be7050 100644
--- a/grpc.gyp
+++ b/grpc.gyp
@@ -98,6 +98,7 @@
           '-fprofile-arcs',
           '-ftest-coverage',
           '-rdynamic',
+          '-lstdc++',
         ],
       }],
       ['grpc_alpine=="true"', {