Log Message:
Update to SBCL 1.3.18

changes in sbcl-1.3.18 relative to sbcl-1.3.17:
  * minor incompatible change: existing values of CFLAGS, ASFLAGS,
    CPPFLAGS, and LINKFLAGS will be incorporated into C compiler
    invocations when building from source.
  * minor incompatible change: the result of WRITE-TO-STRING may be
    a BASE-STRING if all characters written are of type BASE-CHAR.
  * minor incompatible change: the broadcast stream with no output
    streams is a singleton object. That object satisfies OPEN-STREAM-P
    regardless of how many times CLOSE is invoked on it.
  * enhancement: x86[-64] backends contain an experimental feature
    which aids in demonstrating reachability of any object starting
    from a tenured object or a thread stack by producing a proof
    as a sequence of pointers to follow.
    The file "tests/traceroot.test.sh" contains an example usage.
  * enhancement: if the alien symbol "gc_coalesce_string_literals" is
    set to 1 prior to SAVE-LISP-AND-DIE, then similar string constants
    loaded from different fasl files may be collapsed to one object.
    If the variable is set to 2, then additionally strings which are
    STRING= in code resulting from COMPILE can be coalesced.
    For instance, two functions returning the literal string "HI"
    might return EQ strings after collapsing, which may be undesired
    in a particular use. The flag pertains to gencgc only.
  * enhancement: SXHASH values on pathnames are better distributed
  * bug fix: MAKE-PATHNAME removes empty strings as components of a
    directory, as is permitted: "Whenever a pathname is constructed
    the components may be canonicalized if appropriate."
  * optimization: various printer and FORMAT performance enhancements.
  * bug fix: GET-FOREGROUND no longer fails in case all other interactive
    threads exit (lp#1682671, reported by Syll)
  * bug fix: RELEASE-FOREGROUND always removes the current thread from the
    list of interactive threads. (lp#1682867, reported by Syll)