arm: improve error for unsupported IssueSGISignal

Fail early with IllegalOperation if IssueSGISignal is not supported at
all for the platform.

This also helps with verification, because the later range check gets
simplified away automatically, leading to divergent code paths.

Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

src/arch/arm/object/interrupt.c

@@ -95,6 +95,14 @@ exception_t Arch_decodeIRQControlInvocation(word_t invLabel, word_t length,
             current_syscall_error.type = seL4_TruncatedMessage;
             return EXCEPTION_SYSCALL_ERROR;
         }
+
+        // wrap_config_set to prevent verification automation from simplifying it away
+        if (wrap_config_set(NUM_SGIS) == 0) {
+            current_syscall_error.type = seL4_IllegalOperation;
+            userError("IRQControl: IssueSGISignal not available on this platform.");
+            return EXCEPTION_SYSCALL_ERROR;
+        }
+
         word_t irq = getSyscallArg(0, buffer);
         word_t target = getSyscallArg(1, buffer);
         word_t index = getSyscallArg(2, buffer);