[libc] Quiet initializer warnings in getopt

[mcgrathr]

Summary

This prevents -Wmissing-braces warnings.

[michaelrj]

LGTM

libc/src/unistd/getopt.cpp

 
 // This is POSIX compliant and does not support GNU extensions, mainly this is
 // just the re-ordering of argv elements such that unknown arguments can be
 // easily iterated over.
 
 namespace __llvm_libc {
 
 template <typename T> struct RefWrapper {
+  RefWrapper() = delete;
+  constexpr RefWrapper(T *p) : ptr{p} {}
+  constexpr RefWrapper(const RefWrapper &) = default;
   RefWrapper &operator=(const RefWrapper &) = default;
   operator T &() { return *ptr; }
   T &get() { return *ptr; }
   T *ptr;
 };
 
 struct GetoptContext {
   RefWrapper<char *> optarg;