Move core:runtime to base:runtime; keep alias around

base/runtime/os_specific_wasi.odin

@@ -0,0 +1,10 @@
+//+build wasi
+package runtime
+
+import "core:sys/wasm/wasi"
+
+_os_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
+	data := (wasi.ciovec_t)(data)
+	n, err := wasi.fd_write(1, {data})
+	return int(n), _OS_Errno(err)
+}