Use SBCL by default for asdf-tools on Unix
CCL, our previous default, was making `make -f Makefile-lisp-scripting load` unhappy, since CCL's background thread is eating rlwrap's input. Using single-threaded-ccl stops the input race condition, but CCL still puts the tty in raw mode which confused rlwrap and this requires adding a dependency. Still use CCL by default on Windows, since SBCL can't invoke CMD directly.
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