LibC: Enable compiler warnings for scanf and strftime format strings

Libraries/LibC/stdio.h

@@ -101,11 +101,11 @@ int putc(int ch, FILE*);
 int puts(const char*);
 int fputs(const char*, FILE*);
 void perror(const char*);
-int scanf(const char* fmt, ...);
-int sscanf(const char* str, const char* fmt, ...);
-int fscanf(FILE*, const char* fmt, ...);
-int vfscanf(FILE*, const char*, va_list);
-int vsscanf(const char*, const char*, va_list);
+int scanf(const char* fmt, ...) __attribute__((format(scanf, 1, 2)));
+int sscanf(const char* str, const char* fmt, ...) __attribute__((format(scanf, 2, 3)));
+int fscanf(FILE*, const char* fmt, ...) __attribute__((format(scanf, 2, 3)));
+int vfscanf(FILE*, const char*, va_list) __attribute__((format(scanf, 2, 0)));
+int vsscanf(const char*, const char*, va_list) __attribute__((format(scanf, 2, 0)));
 int setvbuf(FILE*, char* buf, int mode, size_t);
 void setbuf(FILE*, char* buf);
 void setlinebuf(FILE*);

Libraries/LibC/time.h

@@ -86,6 +86,6 @@ struct tm* gmtime_r(const time_t* timep, struct tm* result);
 struct tm* localtime_r(const time_t* timep, struct tm* result);
 
 double difftime(time_t, time_t);
-size_t strftime(char* s, size_t max, const char* format, const struct tm*);
+size_t strftime(char* s, size_t max, const char* format, const struct tm*) __attribute__((format(strftime, 3, 0)));
 
 __END_DECLS