diff --git a/library/compiler-builtins/.github/workflows/main.yml b/library/compiler-builtins/.github/workflows/main.yml
index 4e47825b2a27..9071e4ff063d 100644
--- a/library/compiler-builtins/.github/workflows/main.yml
+++ b/library/compiler-builtins/.github/workflows/main.yml
@@ -128,3 +128,18 @@ jobs:
       run: |
         rustup set profile minimal && rustup default "nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/clippy)" && rustup component add clippy
     - run: cargo clippy -- -D clippy::all
+
+  success:
+    needs:
+      - test
+      - rustfmt
+      - clippy
+    runs-on: ubuntu-latest
+    # GitHub branch protection is exceedingly silly and treats "jobs skipped because a dependency
+    # failed" as success. So we have to do some contortions to ensure the job fails if any of its
+    # dependencies fails.
+    if: always() # make sure this is never "skipped"
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: check if any dependency failed
+        run: jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/library/compiler-builtins/README.md b/library/compiler-builtins/README.md
index da0adbce70c6..adcdcacbac12 100644
--- a/library/compiler-builtins/README.md
+++ b/library/compiler-builtins/README.md
@@ -62,7 +62,7 @@ features = ["c"]
 [1]: https://github.com/rust-lang/llvm-project/tree/9e3de9490ff580cd484fbfa2908292b4838d56e7/compiler-rt/test/builtins/Unit
 [2]: https://github.com/rust-lang/llvm-project/tree/9e3de9490ff580cd484fbfa2908292b4838d56e7/compiler-rt/lib/builtins
 [3]: https://github.com/rust-lang/compiler-builtins/blob/0ba07e49264a54cb5bbd4856fcea083bb3fbec15/build.rs#L180-L265
-[4]: https://travis-ci.org/rust-lang/compiler-builtins
+[4]: https://github.com/rust-lang/compiler-builtins/actions
 
 ### Porting Reminders
 
diff --git a/library/compiler-builtins/build.rs b/library/compiler-builtins/build.rs
index c2dd304e759d..6ad7f71538ef 100644
--- a/library/compiler-builtins/build.rs
+++ b/library/compiler-builtins/build.rs
@@ -288,17 +288,23 @@ mod c {
             sources.extend(&[
                 ("__divdc3", "divdc3.c"),
                 ("__divsc3", "divsc3.c"),
-                ("__divxc3", "divxc3.c"),
                 ("__extendhfsf2", "extendhfsf2.c"),
                 ("__muldc3", "muldc3.c"),
                 ("__mulsc3", "mulsc3.c"),
-                ("__mulxc3", "mulxc3.c"),
                 ("__negdf2", "negdf2.c"),
                 ("__negsf2", "negsf2.c"),
-                ("__powixf2", "powixf2.c"),
                 ("__truncdfhf2", "truncdfhf2.c"),
                 ("__truncsfhf2", "truncsfhf2.c"),
             ]);
+
+            if target_arch == "x86" || target_arch == "x86_64" {
+                // Only add 80-bit long double sources on x86.
+                sources.extend(&[
+                    ("__divxc3", "divxc3.c"),
+                    ("__mulxc3", "mulxc3.c"),
+                    ("__powixf2", "powixf2.c"),
+                ]);
+            }
         }
 
         // When compiling in rustbuild (the rust-lang/rust repo) this library
@@ -594,7 +600,12 @@ mod c {
             build_aarch64_out_of_line_atomics_libraries(&src_dir, cfg);
 
             // Some run-time CPU feature detection is necessary, as well.
-            sources.extend(&[("__aarch64_have_lse_atomics", "cpu_model.c")]);
+            let cpu_model_src = if src_dir.join("cpu_model.c").exists() {
+                "cpu_model.c"
+            } else {
+                "cpu_model/aarch64.c"
+            };
+            sources.extend(&[("__aarch64_have_lse_atomics", cpu_model_src)]);
         }
 
         let mut added_sources = HashSet::new();