[FREELDR:UEFI] Implement missing cold reset in Reboot() function (#9092)

- Fix a WARN debug print (Reboot can be called from menu).
- Stabilize reboot fallback abstractions.
- Drop unimplemented path on ARM.

CORE-11954 CORE-17604

boot/freeldr/freeldr/arch/uefi/uefildr.c

@@ -104,15 +104,32 @@ ExecuteLoaderCleanly(PVOID PreviousStack)
     UNREACHABLE;
 }
 
-#ifndef _M_ARM
 DECLSPEC_NORETURN
 VOID __cdecl Reboot(VOID)
 {
-    //TODO: Replace with a true firmware reboot eventually
-    WARN("Something has gone wrong - halting FreeLoader\n");
+    WARN("Performing cold reset\n");
+
+    if (GlobalSystemTable && GlobalSystemTable->RuntimeServices)
+    {
+        /* Attempt a native firmware cold reset */
+        GlobalSystemTable->RuntimeServices->ResetSystem(
+            EfiResetCold,
+            EFI_SUCCESS,
+            0,
+            NULL
+        );
+    }
+
+    /* Fallback dead-loop if runtime services are missing or fail to respond */
     for (;;)
     {
+#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_AMD64))
+        __halt();
+#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+        __asm__ __volatile__("hlt");
+#else
+        /* Fallback placeholder loop for other platforms */
         NOTHING;
+#endif
     }
 }
-#endif

boot/freeldr/freeldr/include/arch/arm/hardware.h

@@ -34,12 +34,6 @@ extern ULONG gDiskReadBuffer, gFileSysBuffer;
 
 #define DriveMapGetBiosDriveNumber(DeviceName) 0
 
-DECLSPEC_NORETURN
-FORCEINLINE VOID Reboot(VOID)
-{
-    DbgBreakPoint();
-}
-
 typedef struct _PAGE_TABLE_ARM
 {
     HARDWARE_PTE_ARMV6 Pte[1024];