runtime/interrupt: add cross-chip disable/restore interrupt support

This should cover all supported baremetal targets.

src/runtime/interrupt/interrupt_tinygoriscv.go

@@ -0,0 +1,29 @@
+// +build tinygo.riscv
+
+package interrupt
+
+import "device/riscv"
+
+// State represents the previous global interrupt state.
+type State uintptr
+
+// Disable disables all interrupts and returns the previous interrupt state. It
+// can be used in a critical section like this:
+//
+//     state := interrupt.Disable()
+//     // critical section
+//     interrupt.Restore(state)
+//
+// Critical sections can be nested. Make sure to call Restore in the same order
+// as you called Disable (this happens naturally with the pattern above).
+func Disable() (state State) {
+	return State(riscv.DisableInterrupts())
+}
+
+// Restore restores interrupts to what they were before. Give the previous state
+// returned by Disable as a parameter. If interrupts were disabled before
+// calling Disable, this will not re-enable interrupts, allowing for nested
+// cricital sections.
+func Restore(state State) {
+	riscv.EnableInterrupts(uintptr(state))
+}