Kernel/riscv64: Implement Processor::pause

Author: https://github.com/spholz
Commit: 58a2e6412c
Pull-request: https://github.com/SerenityOS/serenity/pull/23364
Reviewed-by: https://github.com/ADKaster ✅

Kernel/Arch/riscv64/Processor.h

@@ -196,7 +196,9 @@ ALWAYS_INLINE Thread* ProcessorBase<T>::current_thread()
 template<typename T>
 ALWAYS_INLINE void ProcessorBase<T>::pause()
 {
-    TODO_RISCV64();
+    // FIXME: Use the pause instruction directly (via .option arch, +zihintpause)
+    //        when we upgrade our toolchain to clang 17
+    asm volatile(".word 0x0100000f");
 }
 
 template<typename T>