Makefile: turn any byte-compilation warnings into errors

Makefile

@@ -14,21 +14,23 @@ INIT_PACKAGES="(progn \
       (package-install pkg))) \
   )"
 
+BATCH_W_ERROR = -batch --eval "(setq byte-compile-error-on-warn t)"
+
 all: compile-tests test package-lint clean-elc
 
 package-lint:
-	${EMACS} --eval ${INIT_PACKAGES} -batch -f package-lint-batch-and-exit hcl-mode.el
+	${EMACS} --eval ${INIT_PACKAGES} $(BATCH_W_ERROR) -f package-lint-batch-and-exit hcl-mode.el
 
 hcl-mode.elc: hcl-mode.el Makefile
-	${EMACS} -batch -f batch-byte-compile $<
+	${EMACS} $(BATCH_W_ERROR) -f batch-byte-compile $<
 
 test/test-helper.elc: test/test-helper.el hcl-mode.elc
-	${EMACS} -L . -batch -f batch-byte-compile $<
+	${EMACS} -L . $(BATCH_W_ERROR) -f batch-byte-compile $<
 
 TESTS-EL = test/test-command.el test/test-highlighting.el test/test-indentation.el
 TESTS-ELC = test/test-command.elc test/test-highlighting.elc test/test-indentation.elc
 $(TESTS-ELC): test/test-helper.elc hcl-mode.elc $(TESTS-EL)
-	${EMACS} -L . -l test/test-helper.elc -batch -f batch-byte-compile test/test-command.el test/test-highlighting.el test/test-indentation.el
+	${EMACS} -L . -l test/test-helper.elc $(BATCH_W_ERROR) -f batch-byte-compile test/test-command.el test/test-highlighting.el test/test-indentation.el
 compile-tests: $(TESTS-ELC)
 
 test: $(TESTS-ELC)