Add irq_set_status

irq_set_status can be used to clear the irq status bit so that the
interrupt will stop occuring.

sw/interrupt.h

@@ -9,5 +9,6 @@ void irq_int();
 void nmi_int();
 
 uint8_t irq_get_status();
+void irq_set_status(uint8_t);
 
 #endif

sw/interrupt.s

@@ -9,7 +9,7 @@
 .import   _handle_irq
 
 .export   _irq_int, _nmi_int
-.export   _irq_get_status
+.export   _irq_get_status, _irq_set_status
 
 .include "io.inc65"
 
@@ -51,4 +51,8 @@ break:     JMP break              ; If BRK is detected, something very bad
 _irq_get_status:
            lda IRQ_STATUS
            ldx #$00
+           rts
+
+_irq_set_status:
+           sta IRQ_STATUS
            rts

sw/irq.c

@@ -15,5 +15,6 @@ void handle_irq() {
 
     if (status & BUTTON) {
         puts("Button Interrupt!\n");
+        irq_set_status(status & ~BUTTON);
     }
 }