Array parameters lose alignment metadata and ICE on >16 byte alignments

## Summary There is a bug in `rustc_codegen_nvvm/src/abi.rs` where arrays passed by value to CUDA kernels discard their underlying alignment metadata, forcing them into `PassMode::Direct(ArgAttributes::new())`. This presents two distinct issues: 1. **Lost Alignment Metadata (`IllegalAddress` traps):** If you pass an array of 16-byte aligned elements (like `[u128; 4]` or `[AlignedStruct; 2]`), the compiler forces it to `PassMode::Direct` and generates PTX expecting 8-byte boundaries (e.g., `.param .align 8 .b8 param_0[32]`). However, the Host driver packs the array at a 16-byte boundary. If the kernel subsequently attempts an aligned/vectorized 128-bit load, it can trap with an `IllegalAddress` error. 2. **Internal Compiler Error (ICE) for >16-byte alignments:** Because arrays bypass the 16-byte `PassMode::Cast` workaround that is correctly applied to ADTs, passing an array requiring 32-byte or greater alignment (e.g., `[AlignedStruct32; 2]`) triggers an ICE in the upstream NVPTX ABI handling: `internal error: entered unreachable code: Align is given as power of 2 no larger than 16 bytes`. ## Reproduction Case Define an aligned struct and pass an array of them to a kernel: ```rust #[derive(Copy, Clone)] #[repr(C, align(16))] pub struct AlignedStruct { a: u64, b: u64, } #[cuda_std::kernel] pub unsafe fn array_kernel2(arr: [AlignedStruct; 2], out: *mut u128) { // PTX generates: .param .align 8 .b8 array_kernel2_param_0[32] // The missing 16-byte alignment metadata leads to an ABI mismatch // between the host and device. unsafe { *out = arr[0].a as u128 + arr[1].a as u128; } } ``` If the struct is changed to `#[repr(C, align(32))]`, compiling the kernel causes the compiler to panic with `internal error: entered unreachable code: Align is given as power of 2 no larger than 16 bytes`. ## Issue Details In `crates/rustc_codegen_nvvm/src/abi.rs`, the function `readjust_fn_abi` handles arrays blindly without preserving or checking `arg.layout.align.abi`: ```rust // Current array handling in abi.rs if arg.layout.ty.is_array() && !matches!(arg.mode, PassMode::Direct { .. }) { arg.mode = PassMode::Direct(ArgAttributes::new()); } ``` Unlike the ADT fallback branch (`attrs.pointee_align = Some(arg.layout.align.abi)`), the array block throws away all alignment metadata. It also completely misses the `PassMode::Cast` workaround needed for types with `align >= 16`.