fix: apply build FLAGS correctly

A typo in the dependency variable program_obj_files caused make to fall back to implicit/default rules. FLAGS was ignored because the default behavior is to use CFLAGS.

makefile

@@ -29,7 +29,7 @@ program_obj_files = stack.o bintree.o numbers.o timer.o highscore.o
 doble : main.o $(program_obj_files)
 	$(CC) $(FLAGS) $^ -o doble
 
-$(program_obj_filesobj_files): %.o: %.c
+$(program_obj_files): %.o: %.c
 	$(CC) -c $(FLAGS) $^ -o $@
 
 # --------------------------

timer.c

@@ -1,12 +1,6 @@
 #include "timer.h"
 
-#ifdef __linux__
-// Defines strict posix compliance for CLOCK_MONOTONIC
-#define _POSIX_C_SOURCE 199309L
-#include <time.h>
-#endif
-
-#if __APPLE__ || __linux__
+#if __APPLE__
 #include <sys/time.h>
 static struct timespec start = {0, 0};
 
@@ -27,8 +21,7 @@ double stopTimer()
 
     double measuredSeconds = (double)delta_us / 1000000.;
 
-    if (start.tv_nsec > 0)
-    {
+    if(start.tv_nsec > 0) {
         start.tv_nsec = 0;
         start.tv_sec = 0;
     }