[llvm] [Offload] Add support for riscv64 to host plugin (PR #115773)

[Joseph Huber via llvm-commits]

================
@@ -440,6 +440,8 @@ struct GenELF64PluginTy final : public GenericPluginTy {
 #else
     return llvm::Triple::ppc64;
 #endif
+#elif defined(__riscv) && (__riscv_xlen == 64)
+    return llvm::Triple::ArchType::riscv64;
----------------
jhuber6 wrote:

Is `ArchType` necessary here?

https://github.com/llvm/llvm-project/pull/115773