[CIR][CodeGen] Implement LValue emission for global variable declaration of reference type

[tommymcm]

Minimized test case:

class A {};
class B {
public:
  static A &A;
};
A A() { B::A; }

Failed assertion:

clangir/clang/lib/CIR/CodeGen/CIRGenExpr.cpp

Line 937 in aeac352

assert(0 && "NYI");

Flags: -fclangir -O2