Add LTO test

.github/workflows/release.yml

@@ -71,3 +71,8 @@ jobs:
         # FIXME(antoyo): we cannot enable LTO for stdarch tests currently because of some failing LTO tests using proc-macros.
         echo -n 'lto = "fat"' >> build_system/build_sysroot/Cargo.toml
         EMBED_LTO_BITCODE=1 ./y.sh test --release --clean --release-sysroot --build-sysroot --keep-lto-tests ${{ matrix.commands }}
+
+    - name: Run y.sh cargo build
+      run: |
+        EMBED_LTO_BITCODE=1 CHANNEL="release" ./y.sh cargo build --release --manifest-path tests/hello-world/Cargo.toml
+        # TODO: grep the asm output for "call my_func" and fail if it is found.

tests/hello-world/Cargo.toml

@@ -7,3 +7,6 @@ mylib = { path = "mylib" }
 
 [profile.dev]
 lto = "thin"
+
+[profile.release]
+lto = "fat"