Userland+Tests: Add initial riscv64 support

Author: https://github.com/spholz
Commit: 6824d2a788
Pull-request: https://github.com/SerenityOS/serenity/pull/21139
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Utilities/functrace.cpp

@@ -62,6 +62,11 @@ static void print_syscall(PtraceRegisters& regs, size_t depth)
     (void)begin_color;
     (void)end_color;
     TODO_AARCH64();
+#elif ARCH(RISCV64)
+    (void)regs;
+    (void)begin_color;
+    (void)end_color;
+    TODO_RISCV64();
 #else
 #    error Unknown architecture
 #endif
@@ -142,6 +147,9 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 #elif ARCH(AARCH64)
         const FlatPtr ip = 0; // FIXME
         TODO_AARCH64();
+#elif ARCH(RISCV64)
+        const FlatPtr ip = 0; // FIXME
+        TODO_RISCV64();
 #else
 #    error Unknown architecture
 #endif