Compile `no_std` test using xargo

The `no_std` test disables `std`, so unwinding is unsupported, so we use
`panic = "abort"` but the `core` library is compiled with unwind by
default which breaks the build. Xargo can handle this by recompiling
`core` with `panic = "abort"` so we use it.

.github/workflows/rust.yml

@@ -46,6 +46,8 @@ jobs:
         uses: dtolnay/rust-toolchain@nightly
       - name: Install src
         run: rustup component add rust-src
+      - name: Install xargo
+        run: cargo install xargo
       - name: Running test script
         env:
           DO_FMT: true

contrib/_test.sh

@@ -101,8 +101,10 @@ if [ "$DO_ASAN" = true ]; then
     RUSTFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins -Cforce-frame-pointers=yes -Cllvm-args=-msan-eager-checks=0' \
     cargo test --lib --all --features="$FEATURES" -Zbuild-std --target x86_64-unknown-linux-gnu
 
-    cargo run --release --manifest-path=./no_std_test/Cargo.toml | grep -q "Verified Successfully"
-    cargo run --release --features=alloc --manifest-path=./no_std_test/Cargo.toml | grep -q "Verified alloc Successfully"
+    cd no_std_test
+    xargo run --release --target=x86_64-unknown-linux-gnu | grep -q "Verified Successfully"
+    xargo run --release --target=x86_64-unknown-linux-gnu --features=alloc | grep -q "Verified alloc Successfully"
+    cd -
 fi
 
 # Run formatter if told to.

no_std_test/Xargo.toml

@@ -0,0 +1,2 @@
+[dependencies]
+alloc = {}