chore: compile for CBMC with warnings-as-errors

This will avoid type conflicts from silently creeping in.

Author: tautschnig

Diff for: verification/cbmc/proofs/Makefile.common

@@ -307,8 +307,8 @@ COVERFLAGS += $(CBMC_FLAG_MALLOC_FAIL_NULL)
 NONDET_STATIC ?=
 
 # Flags to pass to goto-cc for compilation and linking
-COMPILE_FLAGS ?= -Wall
-LINK_FLAGS ?= -Wall
+COMPILE_FLAGS ?= -Wall -Werror
+LINK_FLAGS ?= -Wall -Werror
 EXPORT_FILE_LOCAL_SYMBOLS ?= --export-file-local-symbols
 
 # Preprocessor include paths -I...