runtime: check for heap allocations inside interrupts

This is unsafe and should never be done.

src/runtime/interrupt/interrupt_none.go

@@ -23,3 +23,9 @@ func Disable() (state State) {
 // calling Disable, this will not re-enable interrupts, allowing for nested
 // cricital sections.
 func Restore(state State) {}
+
+// In returns whether the system is currently in an interrupt.
+func In() bool {
+	// There are no interrupts, so it can't be in one.
+	return false
+}