refactor: clean up Makefiles

trie/Makefile

@@ -1,12 +1,7 @@
 # https://spin.atomicobject.com/2016/08/26/makefile-c-projects/ was a great
 # base for this Makefile
 
-LIB_FILENAME ?= libtrie.a
-
-BUILD_DIR ?= build
-SRC_DIR ?= src
-TEST_DIR ?= test
-INC_DIRS ?= include
+-include config.mk
 
 LIB := $(BUILD_DIR)/$(LIB_FILENAME)
 
@@ -23,15 +18,7 @@ BINS_TEST := $(OBJS_TEST:%.c.o=%)
 TARGETS_TEST := $(BINS_TEST:%=test-%)
 TARGETS_MEM_TEST := $(BINS_TEST:%=test-mem-%)
 
-INC_FLAGS := $(addprefix -I,$(INC_DIRS))
-
-# -MMD: generate a .d file for every source file. This file can be imported by
-#  make and makes make aware that a header file has been changed, ensuring an
-#  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 -g
-_CFLAGS := $(INC_FLAGS) $(CFLAGS) -Wall -Wextra
+_CFLAGS := $(addprefix -I,$(INC_DIRS)) $(CFLAGS) -Wall -Wextra
 
 .PHONY: all
 all: lib