patch 8.2.2639: build failure when fsync() is not available

Problem:    Build failure when fsync() is not available.
Solution:   Add #ifdef.
diff --git a/src/ui.c b/src/ui.c
index 6c1c1de..a423937 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -50,8 +50,10 @@
 # endif
 
 	mch_write(s, len);
+# if defined(HAVE_FSYNC)
 	if (console && s[len - 1] == '\n')
-	    fsync(1);
+	    vim_fsync(1);
+# endif
 
 # if !defined(MSWIN)
 	if (output_conv.vc_type != CONV_NONE)