Revert "Remove macOS fat archive support from LlvmArchiveBuilder"

This reverts commit 047c7cc.

compiler/rustc_codegen_llvm/src/back/archive.rs

@@ -15,8 +15,8 @@ use crate::errors::{
 use crate::llvm::archive_ro::{ArchiveRO, Child};
 use crate::llvm::{self, ArchiveKind, LLVMMachineType, LLVMRustCOFFShortExport};
 use rustc_codegen_ssa::back::archive::{
-    get_native_object_symbols, ArArchiveBuilder, ArchiveBuildFailure, ArchiveBuilder,
-    ArchiveBuilderBuilder, UnknownArchiveKind,
+    get_native_object_symbols, try_extract_macho_fat_archive, ArArchiveBuilder,
+    ArchiveBuildFailure, ArchiveBuilder, ArchiveBuilderBuilder, UnknownArchiveKind,
 };
 
 use rustc_session::cstore::DllImport;
@@ -66,15 +66,21 @@ impl<'a> ArchiveBuilder<'a> for LlvmArchiveBuilder<'a> {
         archive: &Path,
         skip: Box<dyn FnMut(&str) -> bool + 'static>,
     ) -> io::Result<()> {
-        let archive_ro = match ArchiveRO::open(archive) {
+        let mut archive = archive.to_path_buf();
+        if self.sess.target.llvm_target.contains("-apple-macosx") {
+            if let Some(new_archive) = try_extract_macho_fat_archive(&self.sess, &archive)? {
+                archive = new_archive
+            }
+        }
+        let archive_ro = match ArchiveRO::open(&archive) {
             Ok(ar) => ar,
             Err(e) => return Err(io::Error::new(io::ErrorKind::Other, e)),
         };
         if self.additions.iter().any(|ar| ar.path() == archive) {
             return Ok(());
         }
         self.additions.push(Addition::Archive {
-            path: archive.to_path_buf(),
+            path: archive,
             archive: archive_ro,
             skip: Box::new(skip),
         });