Add working cbmc-primitives regressions with SMT2

Author: Enrico Steffinlongo

regression/cbmc-primitives/exists_assume_6231/test2.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 test2.c
 --pointer-check
 ^EXIT=10$

regression/cbmc-primitives/implication_statement_checks_1/test.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 --div-by-zero-check
 test.c
 ^EXIT=0$

regression/cbmc-primitives/r_w_ok_valid/test-no-cp.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 main.c
 --pointer-check --no-simplify --no-propagation
 ^EXIT=0$

regression/cbmc-primitives/same-object-01/test-no-cp.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 main.c
 --no-simplify --no-propagation
 ^EXIT=0$

regression/cbmc-primitives/same-object-02/test-no-cp.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 main.c
 --no-simplify --no-propagation
 ^EXIT=0$

regression/cbmc-primitives/same-object-04/test-no-cp.desc

@@ -1,4 +1,4 @@
-CORE
+CORE new-smt-backend
 main.c
 --no-simplify --no-propagation
 ^EXIT=0$