bump CBMC dependency to release 6.8.0

Author: kroening

lib/cbmc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 elbtunnel.aig.smv
 --bound 12
 ^EXIT=10$
@@ -14,4 +14,3 @@ elbtunnel.aig.smv
 --
 ^warning: ignoring
 --
-The test fails in MacOS CI with Z3.

regression/ebmc/elbtunnel/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE broken-smt-backend
 smv_toint1.smv
 
 ^\[.*\] toint\(0\) = 0: PROVED .*$

regression/smv/expressions/smv_toint1.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 inside1.sv
 
 ^\[.*\] always 2 inside \{1, 2, 3\}: PROVED .*$

regression/verilog/expressions/inside1.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 signing_cast1.sv
 --module main
 ^\[main\.p0\] always signed'\(1'b1\) == -1: PROVED .*$
@@ -12,4 +12,3 @@ signing_cast1.sv
 --
 ^warning: ignoring
 --
-The width of the operand is not preserved.

regression/verilog/expressions/signing_cast1.desc

@@ -124,6 +124,7 @@ ebmc_solver_factoryt ebmc_solver_factory(const cmdlinet &cmdline)
             std::string("Generated by EBMC ") + EBMC_VERSION,
             "QF_AUFBV",
             smt2_solver.value(),
+            "", // solver binary
             message_handler)};
         }
       };