In SB-GROVEL-UNKNOWN-CONSTANT-CONDITION-P: format control doesn't need to be a string

[Paul F. Dietz]

This code in lisp-build.lisp:

  #+sbcl
  (progn
    (defun sb-grovel-unknown-constant-condition-p (c)
      "Detect SB-GROVEL unknown-constant conditions on older versions of SBCL"
      (and (typep c 'sb-int:simple-style-warning)
           (string-enclosed-p
            "Couldn't grovel for "
            (simple-condition-format-control c)
            " (unknown to the C compiler).")))
    (deftype sb-grovel-unknown-constant-condition ()
      '(and style-warning (satisfies sb-grovel-unknown-constant-condition-p))))

is causing me a problem. If the function is called on a condition in which the format-control slot is a function, not a string, it fails.

Also https://bugs.launchpad.net/sbcl/+bug/1803727 in sbcl launchpad.