Update to SBCL 1.0.56

New in version 1.0.56

  * bug fix: fix copy-structure. When copying from stack to heap,
    garbage could end up in the heap making GC unhappy.
    (Thanks to James Knight, #911027)
  * enhancements
      + SBCL can now be built using Clang.
      + ASDF has been updated 2.20.
  * bug fix: compiler errors when weakening hairy integer types. (#913232)
  * bug fix: don't complain about a too-hairy lexical environment
    for inlining when the function has never been requested for inlining.
    (#963530)

(asau)