Strengthening this test so it fails in release mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45446 91177308-0d34-0410-b5e6-96231b3b80d8

test/CFrontend/2007-09-20-GcrootAttribute.c

 // RUN: %llvmgcc -S -emit-llvm %s -o - | grep llvm.gcroot
 // RUN: %llvmgcc -S -emit-llvm %s -o - | grep llvm.gcroot | count 6
+// RUN: %llvmgcc -S -emit-llvm %s -o - | llvm-as
 
 typedef struct foo_s
 {