[stm32] Fix spurious EXTI interrupt with shared IRQ

In case of multiple event lines with a shared IRQ all enabled handlers
were always called even when the respective event was not triggered.

src/modm/platform/extint/stm32/exti.cpp.in

@@ -20,6 +20,11 @@ Exti::handlers[Exti::Lines] modm_fastdata;
 void Exti::irq(uint32_t mask)
 {
 	uint32_t flags = EXTI->IMR{{"1" if (extended or separate_flags) else ""}} & mask;
+%% if separate_flags
+	flags &= (EXTI->FPR1 & EXTI->FTSR1) | (EXTI->RPR1 & EXTI->RTSR1);
+%% else
+	flags &= EXTI->PR{{"1" if extended else ""}};
+%% endif
 	while(flags)
 	{
 		const uint8_t lmb = 31ul - __builtin_clz(flags);