test-lib: use more compact expression in PIPE prerequisite

Signed-off-by: Ramsay Jones <[email protected]>
Reviewed-by: Jonathan Nieder <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ramsay-jones

t/test-lib.sh

@@ -1062,14 +1062,8 @@ test_i18ngrep () {
 
 test_lazy_prereq PIPE '
 	# test whether the filesystem supports FIFOs
-	case $(uname -s) in
-	CYGWIN*|MINGW*)
-		false
-		;;
-	*)
-		rm -f testfifo && mkfifo testfifo
-		;;
-	esac
+	test_have_prereq !MINGW,!CYGWIN &&
+	rm -f testfifo && mkfifo testfifo
 '
 
 test_lazy_prereq SYMLINKS '