Gate pac_enum with v-trap since only the generated vector table is gated

Author: ia0

riscv-rt/src/interrupts.rs

@@ -71,6 +71,7 @@ pub unsafe extern "C" fn _dispatch_core_interrupt(code: usize) {
 }
 
 // In vectored mode, we also must provide a vector table
+#[cfg(feature = "v-trap")]
 #[riscv::pac_enum(unsafe CoreInterruptNumber)]
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum Interrupt {