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.

configure

@@ -4,7 +4,7 @@ interactive_pkgs=libsdl2-dev
 gem5=false
 qemu=true
 submodules='buildroot linux'
-y=''
+y=
 while getopts gpqt OPT; do
   case "$OPT" in
     g)
@@ -17,7 +17,7 @@ while getopts gpqt OPT; do
       qemu=false
       ;;
     t)
-      interactive_pkgs=''
+      interactive_pkgs=
       y='-y'
       ;;
   esac