ARM: remove annoying #warning

Although done with the best intentions, the usage of #warning in the
ARM build makes it hard to see what's going on, or see any "real"
warnings.

Remove at least this particularly often triggered one, so we can
have a relatively "quiet" build again...

headers/os/arch/arm/arch_debugger.h

@@ -23,9 +23,7 @@ struct arm_debug_cpu_state {
         ulong r14;      /* link register */
         ulong r15;      /* program counter */
         ulong cpsr;
-#if __ARM__
-#warning ARM: missing members!
-#endif
+	// TODO missing members!
 	uint32	dummy;
 } __attribute__((aligned(8)));