mingw: explicitly fflush stdout

For performance reasons `stdout` is buffered by default. That leads to
problems if after printing to `stdout` a read on `stdin` is performed.

For that reason interactive commands like `git clean -i` do not function
properly anymore if the `stdout` is not flushed by `fflush(stdout)` before
trying to read from `stdin`.

So let's precede all reads on `stdin` in `git clean -i` by flushing
`stdout`.

Signed-off-by: 마누엘 <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: 마누엘

builtin/clean.c

@@ -580,6 +580,7 @@ static int *list_and_choose(struct menu_opts *opts, struct menu_stuff *stuff)
 			       clean_get_color(CLEAN_COLOR_RESET));
 		}
 
+		fflush(stdout);
 		if (strbuf_getline_lf(&choice, stdin) != EOF) {
 			strbuf_trim(&choice);
 		} else {
@@ -662,6 +663,7 @@ static int filter_by_patterns_cmd(void)
 		clean_print_color(CLEAN_COLOR_PROMPT);
 		printf(_("Input ignore patterns>> "));
 		clean_print_color(CLEAN_COLOR_RESET);
+		fflush(stdout);
 		if (strbuf_getline_lf(&confirm, stdin) != EOF)
 			strbuf_trim(&confirm);
 		else
@@ -760,6 +762,7 @@ static int ask_each_cmd(void)
 			qname = quote_path_relative(item->string, NULL, &buf);
 			/* TRANSLATORS: Make sure to keep [y/N] as is */
 			printf(_("Remove %s [y/N]? "), qname);
+			fflush(stdout);
 			if (strbuf_getline_lf(&confirm, stdin) != EOF) {
 				strbuf_trim(&confirm);
 			} else {