fix: write phony variable properly

Makefile

@@ -45,11 +45,11 @@ srcs+=$(wildcard ${src_dir}/*.c ${src_dir}/**/*.c)
 headers+=$(wildcard ${src_dir}/*.h ${src_dir}/**/*.h)
 objs+=$(patsubst %.c,${build_dir}/%.o,${srcs})
 
-.PHONY: all
+PHONY += all
 all: ${all_targets}
 	${RM} .lastpthread  # Set that the last build was without pthread
 
-.PHONY: install
+PHONY += install
 install: build ${install_bins_targets} ${install_dir}/lib/libthread.so ${install_dir}/lib/libthread.a
 
 ${install_dir}/lib/libthread.so: ${build_dir}/libthread.so
@@ -64,21 +64,11 @@ ${install_bins_targets}: ${install_dir}/bin/%: ${build_dir}/${tst_dir}/%
 	@mkdir -p $(dir $@)
 	install $^ $@
 
-.PHONY: graphs
-graphs:
-	cd graphs && bash generate_graphs.sh
 
-.PHONY: valgrind
-valgrind: ${valgrind_targets}
-
-.PHONY: ${valgrind_targets}
-${valgrind_targets}: valgrind_%: ${build_dir}/${tst_dir}/%
-	valgrind $^ ${check_argv} --leak-check=full --show-reachable=yes --track-origins=yes
-
-.PHONY: build
+PHONY += build
 build: ${bins_target} ${build_dir}/libthread.so ${build_dir}/libthread.a ${build_dir}/${tst_dir}/51-fibonacci ${build_dir}/${tst_dir}/71-preemption
 
-.PHONY: debug
+PHONY += debug
 debug:
 	$(MAKE) USE_DEBUG=. build
 
@@ -121,18 +111,20 @@ ${build_dir}/%.o: %.c
 	@mkdir -p $(dir $@)
 	${CC} -o $@ -c $^ ${CFLAGS}
 
-.PHONY: compile_flags.txt
+PHONY += compile_flags.txt
 compile_flags.txt:
 	(echo "${CFLAGS} ${LDFLAGS}" | sed 's/ /\n/g') > compile_flags.txt
 
-.PHONY: format
+PHONY += format
 format:
 	clang-format -i ${srcs} ${headers}
 
-.PHONY: check_format
+PHONY += check_format
 check_format:
 	clang-format --dry-run --Werror ${srcs} ${headers}
 
-.PHONY: clean
+PHONY += clean
 clean:
 	${RM} -r build install
+
+.PHONY: $(PHONY)