Release candidate 1 for OpenCilk v2.1.

This new version of OpenCilk includes the following major changes:

• An upgraded compiler, now based on LLVM 16.0.6.
• [Beta feature] New compiler support to target alternative runtime systems without having to modify the compiler codebase.
• A new implementation of reducer hyperobjects in the runtime system, which no longer restricts the number of reducers a Cilk program might use.
• Streamlined support in the runtime system for C++ exceptions.
• Several optimizations and improvements to the stealing logic in the runtime system.
• Revised support in Cilksan to race-detect Cilk programs that use reducers, meaning that Cilksan no longer needs special runtime-system support to race-detect such programs.
• Improved Cilksan support for ARM64.
• Many bug fixes to address issues discovered in the previous version.

You can download and build the new version of OpenCilk from source using the infrastructure repository as follows:

git clone git@github.com:OpenCilk/infrastructure.git
cd infrastructure
tools/get -t opencilk/v2.1-rc1 $(pwd)/opencilk
tools/build $(pwd)/opencilk $(pwd)/build

Please let us know if you encounter any issues with this release candidate.