[FileCheck] Don't scan past the closing CHECK-DAG for CHECK-NOT inside CHECK-DAG

If there's enough data in fron of it the skipped region would just
become arbitrarily large, and we scan for the CHECK-NOT everywhere.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304900 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed