Remove legacy fields from stat struct. NFC

[sbc100]

Musl needs these in order to support the linux kernel but we don't need to use the same ABI in emscripten.

Fixes: #19567

[kleisauke]

This PR broke compatibility with Rust.
https://github.com/rust-lang/libc/blob/8530e6fb1996f3ab41e587df2a2b29c5eaa32ec7/src/unix/linux_like/emscripten/mod.rs#L263-L264
https://github.com/rust-lang/libc/blob/8530e6fb1996f3ab41e587df2a2b29c5eaa32ec7/src/unix/linux_like/emscripten/mod.rs#L270

For example, performing a simple read would result in an OOM due to the changes in the stat struct (ABI mismatch).
https://github.com/rust-lang/rust/blob/e0ba2d038db3afa968e13075b1d6eabd24339708/library/std/src/fs.rs#L253-L254

Standalone reproducer:
src/main.rs:

use std::io;
use std::fs::File;

fn main() -> io::Result<()> {
    fs::read("hello.txt")?;
    Ok(())
}

$ curl https://sh.rustup.rs -sSf | sh -s -- -y --profile minimal --target wasm32-unknown-emscripten --default-toolchain nightly-2023-06-24 --component rust-src
$ source "$HOME/.cargo/env"
$ cargo new foo
$ cd foo
$ cat <<EOT > src/main.rs
use std::io;
use std::fs;

fn main() -> io::Result<()> {
    fs::read("hello.txt")?;
    Ok(())
}
EOT
$ RUSTFLAGS="-Clink-arg=-sNODERAWFS" cargo build --release -Zbuild-std=panic_abort,std --target wasm32-unknown-emscripten
   Compiling core v0.0.0 (...)
   Compiling libc v0.2.146
   ...
   Compiling foo v0.1.0 (...)
    Finished release [optimized] target(s) in 8.96s
$ echo "Hello, world!" > hello.txt
$ node target/wasm32-unknown-emscripten/release/foo.js
memory allocation of 1687607155 bytes failed
Aborted()
...
Node.js v20.3.0
$ echo $?
7

This was originally discovered on wasm-vips' test suite.

Details

memory allocation of 1687599246 bytes failed
Aborted(native code called abort())
  1) foreign
       svgload:
     RuntimeError: Aborted(native code called abort())
      at abort (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:567:10)
      at _abort (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:8180:2)
      at std::sys::unix::abort_internal::he27d3d15008e2a87 (wasm://wasm/0080a6de:wasm-function[2650]:0x16fa3e)
      at std::process::abort::h7669195b6a4c4363 (wasm://wasm/0080a6de:wasm-function[2649]:0x16fa34)
      at std::alloc::rust_oom::h027b9d2aafb59d5a (wasm://wasm/0080a6de:wasm-function[2740]:0x173dae)
      at __rg_oom (wasm://wasm/0080a6de:wasm-function[2741]:0x173dbc)
      at __rust_alloc_error_handler (wasm://wasm/0080a6de:wasm-function[447]:0x21703)
      at alloc::alloc::handle_alloc_error::rt_error::h7270c8e33f70b9e6 (wasm://wasm/0080a6de:wasm-function[2854]:0x17ab38)
      at alloc::alloc::handle_alloc_error::ha3344d8667c57d1d (wasm://wasm/0080a6de:wasm-function[2853]:0x17ab2a)
      at invoke_vii (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:16599:27)
      at std::fs::read::inner::hd4ced50fb263ad9f (wasm://wasm/0080a6de:wasm-function[2706]:0x172747)
      at resvg_parse_tree_from_file (wasm://wasm/0080a6de:wasm-function[365]:0x1935a)
      at vips_foreign_load_svg_file_header (wasm://wasm/0080a6de:wasm-function[224]:0x10b2a)
      at vips_foreign_load_build (wasm://wasm/019056d6:wasm-function[1217]:0xb9d68)
      at vips_object_build (wasm://wasm/019056d6:wasm-function[2579]:0x1ba0f9)
      at vips_cache_operation_buildp (wasm://wasm/019056d6:wasm-function[2744]:0x1c53f4)
      at vips::Image::call(char const*, char const*, vips::Option*, emscripten::val, vips::Image const*) (wasm://wasm/019056d6:wasm-function[177]:0x363bb)
      at invoke_viiiii (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:16621:27)
      at vips::Image::svgload(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&, emscripten::val) (wasm://wasm/019056d6:wasm-function[291]:0x4b662)
      at invoke_viii (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:16511:27)
      at embind_init_my_module()::$_152::__invoke(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&) (wasm://wasm/019056d6:wasm-function[862]:0xa090a)
      at invoke_vii (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:16599:27)
      at emscripten::internal::Invoker<vips::Interpolate, std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&>::invoke(vips::Interpolate (*)(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&), emscripten::internal::BindingType<std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>>, void>::StringStruct*) (wasm://wasm/019056d6:wasm-function[602]:0x8e47c)
      at Function.Image$svgload (eval at newFunc (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:6825:22), <anonymous>:8:10)
      at proto.<computed> [as svgload] (file:///home/kleisauke/wasm-vips/lib/vips-node.mjs:6495:61)
      at Object.svgload (file:///home/kleisauke/wasm-vips/test/unit/test_foreign.js:20:33)
      at fileLoader (file:///home/kleisauke/wasm-vips/test/unit/test_foreign.js:79:33)
      at Context.<anonymous> (file:///home/kleisauke/wasm-vips/test/unit/test_foreign.js:909:5)
      at process.processImmediate (node:internal/timers:478:21)

[sbc100]

That sounds like something that should be fixed downstream in rust? Or am I misunderstanding?

[kleisauke]

Indeed, I just opened PR rust-lang/libc#3282 for this.