fix #35793, assertion failure with union of singletons (#35812)

Author: JeffBezanson

src/cgutils.cpp

@@ -702,7 +702,7 @@ static Type *_julia_struct_to_llvm(jl_codegen_params_t *ctx, jl_value_t *jt, jl_
                 Type *AlignmentType = IntegerType::get(jl_LLVMContext, 8 * al);
                 unsigned NumATy = fsz / al;
                 unsigned remainder = fsz % al;
-                assert(NumATy > 0);
+                assert(al == 1 || NumATy > 0);
                 while (NumATy--)
                     latypes.push_back(AlignmentType);
                 while (remainder--)

test/core.jl

@@ -5961,6 +5961,16 @@ let a33709 = A33709(A33709(nothing))
     @test isnothing(a33709.a.a)
 end
 
+# issue #35793
+struct A35793
+    x::Union{Nothing, Missing}
+end
+let x = A35793(nothing), y = A35793(missing)
+    @test x isa A35793
+    @test x.x === nothing
+    @test y.x === missing
+end
+
 # issue 31583
 a31583 = "a"
 f31583() = a31583 === "a"