Backtrace:
In ice-9/eval.scm:
   177:49 19 (lp (#<procedure 7fffeeba8e20 at ice-9/eval.scm:282:?> ?))
   177:49 18 (lp (#<procedure 7fffeeba8e00 at ice-9/eval.scm:282:?> ?))
   177:49 17 (lp (#<procedure 7fffeeba8de0 at ice-9/eval.scm:282:?> ?))
   177:49 16 (lp (#<procedure 7fffeeba8da0 at ice-9/eval.scm:222:?> ?))
   177:49 15 (lp (#<procedure 7fffeeba8cc0 at ice-9/eval.scm:282:?> ?))
   177:49 14 (lp (#<procedure 7fffeeba8ca0 at ice-9/eval.scm:226:?> ?))
   177:49 13 (lp (#<procedure 7fffeeba8c80 at ice-9/eval.scm:282:?> ?))
   177:49 12 (lp (#<procedure 7fffeeba8c60 at ice-9/eval.scm:226:?> ?))
   177:49 11 (lp (#<procedure 7fffeeba8c40 at ice-9/eval.scm:282:?> ?))
   177:49 10 (lp (#<procedure 7fffeeba8c20 at ice-9/eval.scm:282:?> ?))
   177:49  9 (lp (#<procedure 7fffeeba8c00 at ice-9/eval.scm:282:?> ?))
   177:49  8 (lp (#<procedure 7fffeeba8be0 at ice-9/eval.scm:282:?> ?))
   177:49  7 (lp (#<procedure 7fffeeba8bc0 at ice-9/eval.scm:282:?> ?))
   177:49  6 (lp (#<procedure 7fffeeba8a00 at ice-9/eval.scm:292:?> ?))
   177:49  5 (lp (#<procedure 7fffeeba89e0 at ice-9/eval.scm:282:?> ?))
   177:49  4 (lp (#<procedure 7fffeeba89c0 at ice-9/eval.scm:282:?> ?))
   177:49  3 (lp (#<procedure 7fffeeba89a0 at ice-9/eval.scm:282:?> ?))
   177:32  2 (lp (#<procedure 7fffeeba8980 at ice-9/eval.scm:182:?> ?))
    159:9  1 (_ #(#<directory (guile-user) 7fffefbabf00> #<variab?> ?))
In unknown file:
           0 (string-append "--with-cross-build=" #f)

ERROR: In procedure string-append:
In procedure string-append: Wrong type (expecting string): #f