Calls to varargs functions are broken

[dkolsen-pgi]

Yesterday's rebase broke calls to varargs functions.

void f(int, ...);
void g() {
  f(3, 10, 11, 12);
}

$ clang++ -fclangir -c callvararg.cpp
loc("callvararg.cpp":3:3): error: 'llvm.call' op missing var_callee_type attribute for vararg call
fatal error: error in backend: The pass manager failed to lower CIR to LLVMIR dialect!
[ ... ]

This worked before the rebase. This prevents the use of printf in test programs, which makes it a little harder to test changes.

[smeenai]

Thanks for the catch, @lanza will take a look.