Fix attachInterruptVector, use compiler memory barrier

teensy4/imxrt.h

@@ -173,11 +173,11 @@ enum IRQ_NUMBER_t {
 #ifdef __cplusplus
 extern "C" void (* _VectorsRam[NVIC_NUM_INTERRUPTS+16])(void);
 static inline void attachInterruptVector(IRQ_NUMBER_t irq, void (*function)(void)) __attribute__((always_inline, unused));
-static inline void attachInterruptVector(IRQ_NUMBER_t irq, void (*function)(void)) { _VectorsRam[irq + 16] = function; }
+static inline void attachInterruptVector(IRQ_NUMBER_t irq, void (*function)(void)) { _VectorsRam[irq + 16] = function; asm volatile("": : :"memory"); }
 #else
 extern void (* _VectorsRam[NVIC_NUM_INTERRUPTS+16])(void);
 static inline void attachInterruptVector(enum IRQ_NUMBER_t irq, void (*function)(void)) __attribute__((always_inline, unused));
-static inline void attachInterruptVector(enum IRQ_NUMBER_t irq, void (*function)(void)) { _VectorsRam[irq + 16] = function; }
+static inline void attachInterruptVector(enum IRQ_NUMBER_t irq, void (*function)(void)) { _VectorsRam[irq + 16] = function; asm volatile("": : :"memory"); }
 #endif