Add support for llvm::GlobalValue#hasUnnamedAddr, llvm::GlobalValue#setUnnamedAddr

* Add .dSYM in .gitignore
* support.cpp: LLVMHasUnnamedAddr(v), LLVMSetUnnamedAddr(v, b)
* Ruby: LLVM::GlobalValue unnamed_addr?, unnamed_addr=
* 'Hello, World!' example in sample/