add support for riscv64

[futurejones]

Add support for riscv64 as host architecture.

[parkera]

Thanks @futurejones -- we are working on a brand new set of CMake configs in the package branch over here -- we should rebase this on top of that once it lands.

[jmschonfeld]

I believe @iCharlesHu's changes to the cmake for the package branch will actually remove this manual list of architectures and instead ask the compiler for the architecture (which should eliminate the need for this change and others like it in the future). We should double check to confirm, but hopefully this should "Just Work" with the new cmake setup

[iCharlesHu]

Ditto to what @jmschonfeld said. We are removing this list with #4959 and just ask the compiler at runtime.

[futurejones]

@parkera @jmschonfeld @iCharlesHu
#4959 has now been merged but it appears no changes were made with the use of the SwiftSupport.cmake file.
The file still exists and is is still referenced in the CMakeLists.txt file.
https://github.com/apple/swift-corelibs-foundation/blob/ca3669eb9ac282c649e71824d9357dbe140c8251/CMakeLists.txt#L67
https://github.com/apple/swift-corelibs-foundation/blob/main/cmake/modules/SwiftSupport.cmake

Am I missing something?
Thanks.

[jmschonfeld]

@futurejones that PR was merged into the package branch, which is where ongoing work is taking place to re-core this repo on the new swift-foundation repo. That branch is expected to be merged into main imminently as soon as we resolve the final blockers. You can view the new contents of that file on the package branch at https://github.com/apple/swift-corelibs-foundation/blob/package/cmake/modules/FoundationSwiftSupport.cmake and this is the file that will be merged to main shortly (and you can see in that file that the list of architectures is removed)

[jmschonfeld]

The package branch has now been merged to main so I believe this support should now be available for you on main

[futurejones]

@jmschonfeld Thank you,
Closing this PR as issue has been solved with PR #4959