Inefficient codegen for unimported constructors from other modules

[simonster]

I'm not sure if I should combine this with #10194, but the situation here is worse (we're using jl_apply_generic when we should just do this inline), and also a regression. On 8ad0c1c:

julia> module MyMod
       immutable Constructor; end
       end;

julia> f() = MyMod.Constructor();

julia> @code_llvm f()

define void @julia_f_21577() {
top:
  %0 = alloca [3 x %jl_value_t*], align 8
  %.sub = getelementptr inbounds [3 x %jl_value_t*]* %0, i64 0, i64 0
  %1 = getelementptr [3 x %jl_value_t*]* %0, i64 0, i64 2
  store %jl_value_t* inttoptr (i64 2 to %jl_value_t*), %jl_value_t** %.sub, align 8
  %2 = load %jl_value_t*** @jl_pgcstack, align 8
  %3 = getelementptr [3 x %jl_value_t*]* %0, i64 0, i64 1
  %.c = bitcast %jl_value_t** %2 to %jl_value_t*
  store %jl_value_t* %.c, %jl_value_t** %3, align 8
  store %jl_value_t** %.sub, %jl_value_t*** @jl_pgcstack, align 8
  store %jl_value_t* null, %jl_value_t** %1, align 8
  %4 = load %jl_value_t** inttoptr (i64 4661211688 to %jl_value_t**), align 8
  %5 = icmp eq %jl_value_t* %4, null
  br i1 %5, label %err, label %ok

err:                                              ; preds = %top
  call void @jl_undefined_var_error(%jl_value_t* inttoptr (i64 13212143952 to %jl_value_t*))
  unreachable

ok:                                               ; preds = %top
  store %jl_value_t* %4, %jl_value_t** %1, align 8
  %6 = call %jl_value_t* @jl_apply_generic(%jl_value_t* inttoptr (i64 4628914896 to %jl_value_t*), %jl_value_t** %1, i32 1)
  %7 = load %jl_value_t** %3, align 8
  %8 = getelementptr inbounds %jl_value_t* %7, i64 0, i32 0
  store %jl_value_t** %8, %jl_value_t*** @jl_pgcstack, align 8
  ret void
}

On 0.3:

julia> @code_llvm f()

define %jl_value_t* @julia_f_20275() {
top:
  ret %jl_value_t* inttoptr (i64 140463055669032 to %jl_value_t*), !dbg !682
}