nintendoswitch: Add experimental Nintendo Switch support without CRT

Bare minimal nintendo switch support using LLD

src/runtime/runtime_nintendoswitch_heap.go

@@ -0,0 +1,31 @@
+// +build nintendoswitch
+
+// +build gc.conservative gc.leaking
+
+package runtime
+
+import "unsafe"
+
+const heapSize = 0x2000000 * 16 // Default by libnx
+
+//go:extern _stack_top
+var stackTopSymbol [0]byte
+
+var (
+	heapStart = uintptr(0)
+	heapEnd   = uintptr(0)
+	stackTop  = uintptr(unsafe.Pointer(&stackTopSymbol))
+)
+
+//export setHeapSize
+func setHeapSize(addr *uintptr, length uint64) uint64
+
+func preinit() {
+	setHeapSize(&heapStart, heapSize)
+
+	if heapStart == 0 {
+		panic("failed to allocate heap")
+	}
+
+	heapEnd = heapStart + heapSize
+}