fix PR7280 by making the warning on code like this:

fix PR7280 by making the warning on code like this:

int test1() {
  return;
}

default to an error.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@108108 91177308-0d34-0410-b5e6-96231b3b80d8