Add arena_free()

Makefile

@@ -1,6 +1,28 @@
 
-CC := gcc
-CFLAGS := -g -O3 -std=c2x -Wall -Wextra -Wpedantic -Werror -Iinclude
+all:
+
+BUILD ?= debug
+COMPILER ?= gcc
+
+# ==== set compiler flags ====
+# credits Maxim Egorushkin:
+# https://stackoverflow.com/questions/48791883/best-practice-for-building-a-make-file/48793058#48793058
+
+CC := $(COMPILER)
+
+# -fsanitize={address,undefined}
+CFLAGS.gcc.debug := -Og -ggdb -pg -fsanitize=address -fno-omit-frame-pointer
+CFLAGS.gcc.release := -O3 -g -march=native -DNDEBUG
+CFLAGS.gcc := -fanalyzer
+
+CFLAGS.clang.debug :=-O0 -g3 -DBACKTRACE -rdynamic
+CFLAGS.clang.release :=-O3 -g -march=native -DNDEBUG
+CFLAGS.clang :=
+
+CFLAGS := ${CFLAGS.${COMPILER}} ${CFLAGS.${COMPILER}.${BUILD}} \
+		  -Iinclude \
+		  -std=c2x \
+		  -Wall -Wextra -Wpedantic -Werror
 
 BUILD_DIR := build
 BIN_DIR := lib
@@ -9,6 +31,8 @@ TEST_DIR := test
 OBJS := $(BUILD_DIR)/arena.o
 FPIC_OBJS := $(BUILD_DIR)/fpic/arena.o
 
+all : static
+
 static : $(BIN_DIR)/libarena.a
 
 dynamic : $(BIN_DIR)/libarena.so
@@ -22,7 +46,7 @@ $(BIN_DIR)/libarena.a : $(OBJS) | $(BIN_DIR)
 	ar cr $@ $^
 
 $(BIN_DIR)/libarena.so : $(FPIC_OBJS) | $(BIN_DIR)
-	$(CC) -shared -o $@ $^
+	$(CC) -o $@ -shared $(CFLAGS) $^
 
 $(BUILD_DIR)/%.o : src/%.c | $(BUILD_DIR)
 	$(CC) -o $@ -c $(CFLAGS) $<