Add -Werror flag in the build process (#203)

* Add -Werror flag in the build process
* Add -Werror to link flags

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Signed-off-by: Felipe R. Monteiro <felisous@amazon.com>

src/cbmc_starter_kit/template-for-repository/proofs/Makefile.common

@@ -299,8 +299,8 @@ CHECKFLAGS += $(CBMC_FLAG_UNSIGNED_OVERFLOW_CHECK)
 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
 
 # During instrumentation, it adds models of C library functions