turn on overflow checking, will work once diffblue/cbmc#4666 is merged

Author: danielsn

.cbmc-batch/jobs/Makefile.common

@@ -37,7 +37,7 @@ CBMCFLAGS += --pointer-check
 CBMCFLAGS += --pointer-overflow-check
 CBMCFLAGS += --signed-overflow-check
 CBMCFLAGS += --undefined-shift-check
-#CBMCFLAGS += --unsigned-overflow-check
+CBMCFLAGS += --unsigned-overflow-check
 CBMCFLAGS += --unwind 1
 CBMCFLAGS += --unwinding-assertions
 CBMCFLAGS += $(CBMC_UNWINDSET)

.cbmc-batch/jobs/aws_hash_c_string/cbmc-batch.yaml

@@ -1,4 +1,4 @@
 jobos: ubuntu16
-cbmcflags: "--bounds-check;--div-by-zero-check;--float-overflow-check;--nan-check;--pointer-check;--pointer-overflow-check;--signed-overflow-check;--undefined-shift-check;--unwind;1;--unwinding-assertions;--unwindset;strlen.0:257,hashlittle2.2:22;--object-bits;8"
+cbmcflags: "--bounds-check;--div-by-zero-check;--float-overflow-check;--nan-check;--pointer-check;--pointer-overflow-check;--signed-overflow-check;--undefined-shift-check;--unsigned-overflow-check;--unwind;1;--unwinding-assertions;--unwindset;strlen.0:257,hashlittle2.2:22;--object-bits;8"
 goto: aws_hash_c_string_harness.goto
 expected: "SUCCESSFUL"