Make IdentifierResolver::isDeclInScope regard declarations of a parent...

Make IdentifierResolver::isDeclInScope regard declarations of a parent 'control' scope as part of the current scope.
The 'control' scope is the 'condition' scope of if/switch/while statements and the scope that contains the for-init-statement and 'condition' of a for statement.

e.g:
if (int x = 0 /*'control' scope*/) {
  // x will be regarded as part of this substatement scope.
} else {
  // and as part of this substatement scope too.
}

llvm-svn: 56020