Fix a linkage error with mac clang
Prevent symbol cache variables from being instantiated multipe times.
diff --git a/src/ruby/ext/grpc/rb_grpc.c b/src/ruby/ext/grpc/rb_grpc.c
index 51d1872..4b1015f 100644
--- a/src/ruby/ext/grpc/rb_grpc.c
+++ b/src/ruby/ext/grpc/rb_grpc.c
@@ -257,6 +257,11 @@
VALUE grpc_rb_mGRPC = Qnil;
VALUE grpc_rb_mGrpcCore = Qnil;
+/* cached Symbols for members in Status struct */
+VALUE sym_code = Qundef;
+VALUE sym_details = Qundef;
+VALUE sym_metadata = Qundef;
+
void Init_grpc() {
grpc_init();
ruby_vm_at_exit(grpc_rb_shutdown);