Split crates requiring nightly Rust into separate unstable workspace

Fixes: immunant#1220

Author: joshtriplett

.github/workflows/internal-testsuite.yml

@@ -104,12 +104,13 @@ jobs:
       run: |
         export LLVM_CONFIG_PATH=/usr/bin/llvm-config-15
         cargo build --release
+        (cd unstable && cargo build --release)
 
     # TODO(pl): figure out why compile_commands.json may cause json-c to fail
     - name: Run c2rust testsuite
       run: |
         find testsuite -type f -name compile_commands.json -delete
-        export PATH=$PWD/target/release:$HOME/.local/bin:$PATH
+        export PATH=$PWD/target/release:$PWD/unstable/target/release:$HOME/.local/bin:$PATH
         echo "PATH=$PATH"
         python3 testsuite/test.py curl json-c lua nginx zstd
 

.gitignore

@@ -14,6 +14,7 @@
 **/compile_commands.json
 **/Cargo.lock
 !/Cargo.lock
+!/unstable/Cargo.lock
 .python-version
 .clangd
 # ignore Clion build dirs