Correctly embed the bitcode when compiling the sysroot

Author: antoyo

.github/workflows/release.yml

@@ -75,8 +75,6 @@ jobs:
     - name: Run tests
       run: |
         # FIXME(antoyo): we cannot enable LTO for stdarch tests currently because of some failing LTO tests using proc-macros.
-        # FIXME(antoyo): this should probably not be needed since we embed the LTO bitcode.
-        printf '[profile.release]\nlto = "fat"\n' >> build/build_sysroot/sysroot_src/library/Cargo.toml
         ./y.sh test --release --clean --release-sysroot --build-sysroot --keep-lto-tests ${{ matrix.commands }}
 
     - name: LTO test

build_system/src/build.rs

@@ -108,6 +108,7 @@ pub fn build_sysroot(env: &HashMap<String, String>, config: &ConfigInfo) -> Resu
     if config.sysroot_panic_abort {
         rustflags.push_str(" -Cpanic=abort -Zpanic-abort-tests");
     }
+    rustflags.push_str(" -Cembed-bitcode=yes");
     rustflags.push_str(" -Z force-unstable-if-unmarked");
     if config.no_default_features {
         rustflags.push_str(" -Csymbol-mangling-version=v0");