chore: make lint job check for warnings

.woodpecker/lint.yml

@@ -11,5 +11,6 @@ pipeline:
     pull: true
     commands:
       - make lint
+      - make CFLAGS='-Werror'
     when:
       event: [push, pull_request]

Makefile

@@ -25,8 +25,8 @@ INC_FLAGS := $(addprefix -I,$(INC_DIRS))
 #  object file is also recompiled if only a header is changed.
 # -MP: generate a dummy target for every header file (according to the  docs it
 #  prevents some errors when removing header files)
-CFLAGS ?= -MMD -MP -Wall -Wextra
-CFLAGS += $(INC_FLAGS)
+CFLAGS ?= -MMD -MP
+VIETERCFLAGS := $(INC_FLAGS) $(CFLAGS) -Wall -Wextra
 
 .PHONY: all
 all: vieter
@@ -40,7 +40,7 @@ $(BUILD_DIR)/$(LIB_FILENAME): $(OBJS)
 
 $(BUILD_DIR)/$(SRC_DIR)/%.c.o: $(SRC_DIR)/%.c
 	mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(VIETERCFLAGS) -c $< -o $@
 
 
 # =====TESTING=====
@@ -67,7 +67,7 @@ $(BINS_TEST): %: %.c.o $(OBJS)
 # exposed.
 $(BUILD_DIR)/$(TEST_DIR)/%.c.o: $(TEST_DIR)/%.c
 	mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -I$(TEST_DIR) \
+	$(CC) $(VIETERCFLAGS) -I$(TEST_DIR) \
 		-I$(dir $(@:$(BUILD_DIR)/$(TEST_DIR)/%=$(SRC_DIR)/%)) \
 		-c $< -o $@