Reviewed GLFW issue with ppoll() function

src/Makefile

@@ -348,7 +348,7 @@ endif
 #  -Wstrict-prototypes      warn if a function is declared or defined without specifying the argument types
 #  -Werror=implicit-function-declaration   catch function calls without prior declaration
 ifeq ($(PLATFORM),PLATFORM_DESKTOP)
-    #CFLAGS += -Werror=implicit-function-declaration
+    CFLAGS += -Werror=implicit-function-declaration
 endif
 ifeq ($(PLATFORM),PLATFORM_WEB)
     # -Os                        # size optimization

src/external/glfw/src/posix_poll.c

@@ -29,7 +29,7 @@
 #define _GNU_SOURCE
 
 #include "internal.h"
-#include "posix_poll.h"
+#include "posix_poll.h"     // @raysan5: Required for poll(), ppoll()
 
 #include <signal.h>
 #include <time.h>

src/external/glfw/src/posix_poll.h

@@ -26,6 +26,7 @@
 // It is fine to use C99 in this file because it will not be built with VS
 //========================================================================
 
+#define _GNU_SOURCE     // @raysan5: Required for ppoll()
 #include <poll.h>
 
 GLFWbool _glfwPollPOSIX(struct pollfd* fds, nfds_t count, double* timeout);