Fix ABI compatibility with Emscripten >= 3.1.42

See:
emscripten-core/emscripten#19569 (comment)

build.rs

@@ -7,6 +7,7 @@ use std::string::String;
 // 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",
     "freebsd10",
     "freebsd11",
     "freebsd12",
@@ -69,6 +70,18 @@ fn main() {
         Some(_) | None => set_cfg("freebsd11"),
     }
 
+    match emcc_version() {
+        Some((major, minor, patch))
+            if (major > 3)
+                || (major == 3 && minor > 1)
+                || (major == 3 && minor == 1 && patch >= 42) =>
+        {
+            set_cfg("emscripten_new_stat_abi")
+        }
+        // Non-Emscripten or version < 3.1.42.
+        Some(_) | None => (),
+    }
+
     // On CI: deny all warnings
     if libc_ci {
         set_cfg("libc_deny_warnings");
@@ -238,6 +251,33 @@ fn which_freebsd() -> Option<i32> {
     }
 }
 
+fn emcc_version() -> Option<(u32, u32, u32)> {
+    let output = std::process::Command::new("emcc")
+        .arg("-dumpversion")
+        .output()
+        .ok();
+    if output.is_none() {
+        return None;
+    }
+    let output = output.unwrap();
+    if !output.status.success() {
+        return None;
+    }
+
+    let stdout = String::from_utf8(output.stdout).ok();
+    if stdout.is_none() {
+        return None;
+    }
+    let version = stdout.unwrap();
+    let mut pieces = version.trim().split('.');
+
+    let major = pieces.next()?.parse().unwrap();
+    let minor = pieces.next()?.parse().unwrap();
+    let patch = pieces.next()?.parse().unwrap();
+
+    Some((major, minor, patch))
+}
+
 fn set_cfg(cfg: &str) {
     if !ALLOWED_CFGS.contains(&cfg) {
         panic!("trying to set cfg {}, but it is not in ALLOWED_CFGS", cfg);

src/unix/linux_like/emscripten/mod.rs

@@ -260,13 +260,16 @@ s! {
     }
     pub struct stat {
         pub st_dev: ::dev_t,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_dev_padding: ::c_int,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_ino_truncated: ::c_long,
         pub st_mode: ::mode_t,
         pub st_nlink: ::nlink_t,
         pub st_uid: ::uid_t,
         pub st_gid: ::gid_t,
         pub st_rdev: ::dev_t,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_rdev_padding: ::c_int,
         pub st_size: ::off_t,
         pub st_blksize: ::blksize_t,
@@ -282,13 +285,16 @@ s! {
 
     pub struct stat64 {
         pub st_dev: ::dev_t,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_dev_padding: ::c_int,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_ino_truncated: ::c_long,
         pub st_mode: ::mode_t,
         pub st_nlink: ::nlink_t,
         pub st_uid: ::uid_t,
         pub st_gid: ::gid_t,
         pub st_rdev: ::dev_t,
+        #[cfg(not(emscripten_new_stat_abi))]
         __st_rdev_padding: ::c_int,
         pub st_size: ::off_t,
         pub st_blksize: ::blksize_t,