codegen: fix alignment typos (#55880)

So easy to type jl_datatype_align to get the natural alignment instead
of julia_alignment to get the actual alignment. This should fix the
Revise workload.

Change is visible with
```
julia> code_llvm(Random.XoshiroSimd.forkRand, (Random.TaskLocalRNG, Base.Val{8}))
```

src/cgutils.cpp

@@ -3637,6 +3637,8 @@ static void union_alloca_type(jl_uniontype_t *ut,
             },
             (jl_value_t*)ut,
             counter);
+    if (align > JL_HEAP_ALIGNMENT)
+        align = JL_HEAP_ALIGNMENT;
 }
 
 static AllocaInst *try_emit_union_alloca(jl_codectx_t &ctx, jl_uniontype_t *ut, bool &allunbox, size_t &min_align, size_t &nbytes)

src/codegen.cpp

@@ -5151,7 +5151,7 @@ static jl_cgval_t emit_call_specfun_other(jl_codectx_t &ctx, bool is_opaque_clos
                     Value *val = arg.V;
                     SmallVector<Value*,0> roots(arg.inline_roots);
                     if (roots.empty())
-                        std::tie(val, roots) = split_value(ctx, arg, Align(jl_datatype_align(jt)));
+                        std::tie(val, roots) = split_value(ctx, arg, Align(julia_alignment(jt)));
                     AllocaInst *proots = emit_static_roots(ctx, roots.size());
                     for (size_t i = 0; i < roots.size(); i++)
                         ctx.builder.CreateAlignedStore(roots[i], emit_ptrgep(ctx, proots, i * sizeof(void*)), Align(sizeof(void*)));
@@ -7859,7 +7859,7 @@ static jl_returninfo_t get_specsig_function(jl_codectx_t &ctx, Module *M, Value
             }
             props.cc = jl_returninfo_t::SRet;
             props.union_bytes = jl_datatype_size(jlrettype);
-            props.union_align = props.union_minalign = jl_datatype_align(jlrettype);
+            props.union_align = props.union_minalign = julia_alignment(jlrettype);
             // sret is always passed from alloca
             assert(M);
             fsig.push_back(rt->getPointerTo(M->getDataLayout().getAllocaAddrSpace()));