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.

gem5/build

@@ -1,8 +1,8 @@
 #/usr/bin/env bash
 set -eu
 arch=x86_64
-cross_compile=''
-j=''
+cross_compile=
+j=
 while getopts a:c:j: OPT; do
   case "$OPT" in
     a)