Add a fixit suggest for missing case keywords inside a switch scope. For instance...

Add a fixit suggest for missing case keywords inside a switch scope.  For instance, in the following code, 'case ' will be suggested before the '1:'

switch (x) {
  1: return 0;
  default: return 1;
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129943 91177308-0d34-0410-b5e6-96231b3b80d8