cwriter: add the blank wasm util and writer for building pass

cwriter/util_wasm.go

@@ -0,0 +1,6 @@
+//go:build wasm || js
+
+package cwriter
+
+// There is no ioctl on wasm, so we just use a dummy value.
+const ioctlReadTermios = 0

cwriter/writer_posix.go

@@ -1,4 +1,4 @@
-//go:build !windows
+//go:build !windows && !js && !wasm
 
 package cwriter
 

cwriter/writer_wasm.go

@@ -0,0 +1,21 @@
+//go:build js || wasm
+
+package cwriter
+
+// We can not use writer in wasm, so we just use a dummy value.
+type Writer struct {
+}
+
+func (w *Writer) Flush(lines int) error {
+	return nil
+}
+
+// GetSize returns the dimensions of the given terminal.
+func GetSize(fd int) (width, height int, err error) {
+	return 0, 0, nil
+}
+
+// IsTerminal returns whether the given file descriptor is a terminal.
+func IsTerminal(fd int) bool {
+	return true
+}