x86: UV, SGI RTC: add generic system vector, build fix on UP

Make ack_APIC_irq() build on !SMP && !APIC too.

Cc: Dimitri Sivanich <sivanich@sgi.com>
LKML-Reference: <20090304185605.GA24419@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/apic.h

@@ -379,13 +379,15 @@ static inline u32 safe_apic_wait_icr_idle(void)
 
 static inline void ack_APIC_irq(void)
 {
+#ifdef CONFIG_X86_LOCAL_APIC
 	/*
 	 * ack_APIC_irq() actually gets compiled as a single instruction
 	 * ... yummie.
 	 */
 
 	/* Docs say use 0 for future compatibility */
 	apic_write(APIC_EOI, 0);
+#endif
 }
 
 static inline unsigned default_get_apic_id(unsigned long x)