treewide: Make still dont* Variables are optional in most cases

Go beyond the obvious setup hooks now, with a bit of sed, with a skipped case:

 - cc-wrapper's `dontlink`, because it already is handled.

Also, in nix files escaping was manually added.

EMP

pkgs/development/interpreters/python/hooks/python-remove-bin-bytecode-hook.sh

@@ -12,6 +12,6 @@ pythonRemoveBinBytecodePhase () {
     fi
 }
 
-if [ -z "$dontUsePythonRemoveBinBytecode" ]; then
+if [ -z "${dontUsePythonRemoveBinBytecode-}" ]; then
     preDistPhases+=" pythonRemoveBinBytecodePhase"
 fi