implement sizeof/alignof support for structs, unions and complex.

implement sizeof/alignof support for structs, unions and complex.

This allows us to compile this:

struct abc { char A; double D; };

int foo() {
  return sizeof(struct abc);
  return __alignof__(struct abc);
}

Into:

        ret i32 16
        ret i32 8

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@40010 91177308-0d34-0410-b5e6-96231b3b80d8