Changes simulation ending mechanism (exit function)

As higher optimization might actually schedule a jump to self while waiting for timer interrupts this is a more robust implementation in that sense

port/moonlight/src/bootup.c

@@ -10,6 +10,7 @@
 #include <string.h>
 #include <picotls.h>
 #include <tx_port.h>
+#include <riscv-csr.h>
 #ifdef __cplusplus
 #define EXTERN_C extern "C"
 #else
@@ -121,10 +122,9 @@ void _initialize(void) {
 // This should never be called. Busy loop with the CPU in idle state.
 void _exit(int exit_code) {
     (void)exit_code;
-    // Halt
+    csr_clr_bits_mie(MIE_MTI_BIT_MASK);
+    csr_clr_bits_mstatus(MSTATUS_MIE_BIT_MASK);
     while (1) {
         __asm__ volatile ("wfi");
-        // Incase periodic interrupts are scheduled (e.g. timer), additionaly jump to self
-        for (;;);
     }
 }