libc: Add stubs for fflush() and ungetc()

libc/include/stdio.h

@@ -101,6 +101,9 @@ extern "C"
     /* Read a character from standard input. */
     int getchar(void);
 
+    /* Push a character back to stream so that it can be read again. */
+    int ungetc(int c, FILE* stream);
+
     /* Read a line from stream. */
     char* fgets(char* buf, size_t size, FILE* stream);
 

libc/src/stdio.cpp

@@ -46,6 +46,12 @@ static int fdopen_check_compatible_mode(int fd, int new_flags)
 
 extern "C"
 {
+    int fflush(FILE*)
+    {
+        // FIXME: Files are not buffered right now.
+        return 0;
+    }
+
     FILE* fopen(const char* path, const char* mode)
     {
         int flags;
@@ -479,4 +485,9 @@ extern "C"
         if (!f) close(fd);
         return f;
     }
+
+    int ungetc(int, FILE*)
+    {
+        fail("FIXME: ungetc: not implemented");
+    }
 }