Attached Swift 5.6 patches for RISCV64.

Failing to build StdLib due to being unable to pass `-mno-relax` to the Swift compiler / linker.

ld.lld: error: stdlib/public/core/LINUX/riscv64/Swift.o: cannot link object files with different floating-point ABI
ld.lld: error: Swift.o🙁.text+0x0): relocation R_RISCV_ALIGN requires unimplemented linker relaxation; recompile with -mno-relax

@buttaface Do you have any suggestions? Everything from the compiler to the StdLib is building, but its failing at the linking stage. Passing `-mno-relax` to the Cmake C Flags fixes all C and C++ linking (e.g. libdispatch and Swift Runtime) but not sure how to pass to C compiler.

CodaFi (JIRA User) I have tried a lot of options based on your document https://gist.github.com/CodaFi/b1e0d0f37cd2890c07c5 and passing them via `
-DSWIFT_STDLIB_EXTRA_SWIFT_COMPILE_FLAGS` to cmake for cross compiling the StdLib.

There is a function in the CMake configuration for the stdlib where we add platform-specific link flags when needed, you could try adding it there.

@buttaface Your suggestion helped me overcome the linking issue. Now my issue is that my C nd C++ code is being compiled with hard float (double) but the Swift code is not. Swift doesn't have the `-march`, `-mabi` `-mcpu` flags that Clang does. To my knowledge, based on review of Clang's code, when targeting Linux and RISCV64, if none of that is specified, it will default to lp64d .

I can attempt to build the Linux image with Soft Float ABI, but there will be a significant performance penalty. Also pretty much all RISC64 cores available to buy have double Float support, hence why Buildroot makes it the default.

(bullseye)root@mac-mini:/home/coleman/Developer/buildroot# /usr/sbin/chroot ./output/target/ /usr/bin/qemu-riscv64-static /usr/bin/hello
Hello, world!

I got the RISCV64 Soft Float build working.

https://github.com/MillerTechnologyPeru/swift/releases/tag/swift-5.6-RC1-RISCV

#42055

Opened new PRs

#61815
apple/swift-tools-support-core#360