Test: unconstrained pointer need not be dynamic object

Depending on the model returned by the solver, the unconstrained
pointer could fail one of several assertions: it need not be a dynamic
object, and the test specification should accept that.

Author: tautschnig

regression/cbmc-library/free-01/test.desc

@@ -1,7 +1,7 @@
 CORE
 main.c
 --pointer-check --bounds-check --stop-on-fail
-free argument must be NULL or valid pointer
+free argument must be (NULL or valid pointer|dynamic object)
 ^EXIT=10$
 ^SIGNAL=0$
 ^VERIFICATION FAILED$