Create the cli.gitignore mechanism to pass extra default cli options

Document that X11 mouse is not moving.

Convert x='' to x= on all scripts, and also fix case ;; indentations.

Add dummy value to QEMU's -trace enable= to prevent warning.

Expand built-in package choice rationale.

common

@@ -17,3 +17,7 @@ set_common_vars() {
   qemu_out_dir="${out_arch_dir}/qemu"
   common_dir="${out_dir}/common"
 }
+f=cli.gitignore
+if [ -f "$f" ]; then
+  . "$f"
+fi