cc-wrapper: Unconditionally use @infixSalt@ accross the board

This is basically a sed job, in preparation of the next commit. The
rules are more or less:

  - s"NIX_(.._WRAPPER_)?([a-zA-Z0-9@]*)"NIX_\1@infixSalt@_\2"g

  - except for non-cc-wrapper-specific vars like `NIX_DEBUG`