build: make rclone build with wasm

Needed to drop
- azureblob backend
- cache backend
- qingstor backend
- cachestats command
- ncdu command

lib/terminal/terminal_unsupported.go

@@ -0,0 +1,23 @@
+//+build js
+
+package terminal
+
+import "errors"
+
+// GetSize reads the dimensions of the current terminal or returns a
+// sensible default
+func GetSize() (w, h int) {
+	return 80, 25
+}
+
+// IsTerminal returns whether the fd passed in is a terminal or not
+func IsTerminal(fd int) bool {
+	return false
+}
+
+// ReadPassword reads a line of input from a terminal without local echo. This
+// is commonly used for inputting passwords and other sensitive data. The slice
+// returned does not include the \n.
+func ReadPassword(fd int) ([]byte, error) {
+	return nil, errors.New("can't read password")
+}