emscripten: Assume version is at least 3.1.42

This revises commit 63b0d67
to assume that Emscripten 3.1.42 or later is being used whenever
`emcc` is not available. Since Emscripten 3.1.42 was released on
June 23, 2023, the majority of users are expected to have upgraded
to a more recent version.

Resolves: rust-lang/rust#131467.

(backport <rust-lang#4243">)
(cherry picked from commit b511f66)

Author: kleisauke

build.rs

@@ -5,7 +5,7 @@ use std::{env, str};
 // need to know all the possible cfgs that this script will set. If you need to set another cfg
 // make sure to add it to this list as well.
 const ALLOWED_CFGS: &'static [&'static str] = &[
-    "emscripten_new_stat_abi",
+    "emscripten_old_stat_abi",
     "espidf_time32",
     "freebsd10",
     "freebsd11",
@@ -74,9 +74,9 @@ fn main() {
     }
 
     match emcc_version_code() {
-        Some(v) if (v >= 30142) => set_cfg("emscripten_new_stat_abi"),
-        // Non-Emscripten or version < 3.1.42.
-        Some(_) | None => (),
+        Some(v) if (v < 30142) => set_cfg("emscripten_old_stat_abi"),
+        // Non-Emscripten or version >= 3.1.42.
+        _ => (),
     }
 
     // On CI: deny all warnings

src/unix/linux_like/emscripten/mod.rs

@@ -227,16 +227,16 @@ s! {
     }
     pub struct stat {
         pub st_dev: crate::dev_t,
-        #[cfg(not(emscripten_new_stat_abi))]
+        #[cfg(emscripten_old_stat_abi)]
         __st_dev_padding: c_int,
-        #[cfg(not(emscripten_new_stat_abi))]
+        #[cfg(emscripten_old_stat_abi)]
         __st_ino_truncated: c_long,
         pub st_mode: crate::mode_t,
         pub st_nlink: crate::nlink_t,
         pub st_uid: crate::uid_t,
         pub st_gid: crate::gid_t,
         pub st_rdev: crate::dev_t,
-        #[cfg(not(emscripten_new_stat_abi))]
+        #[cfg(emscripten_old_stat_abi)]
         __st_rdev_padding: c_int,
         pub st_size: off_t,
         pub st_blksize: crate::blksize_t,