Allow variable names to be quoted with -var-list-children

Allow both '-var-list-children var0' and '-var-list-children "var0"' to be used with the -var-list-children command. GDB MI allows for this and it is necessary if the variable name contains spaces, such as var5.std::_Vector_base<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<cahr> > > >.

Differential Revision: http://reviews.llvm.org/D15168

llvm-svn: 254941