[Makefile.PL] Fix git ls-files on windows.

Makefile.PL

@@ -4,7 +4,7 @@ if (-d ".git") { # Are we in our development tree? If so, create MANIFEST.
     my ($dir, $manifest);
     open $manifest, ">", "MANIFEST" or die "MANIFEST: $!";
     print $manifest "MANIFEST\n";
-    open $dir, '-|', 'git', 'ls-files' or die "Couldn't run git: $!";
+    open $dir, 'git ls-files|' or die "Couldn't run git: $!";
     while (<$dir>) { print $manifest $_ unless /^\.|^monotonic_clock/ }
     open $dir, '-|', 'cd monotonic_clock && git ls-files' or die "Couldn't run git in monotonic_clock: $!";
     while (<$dir>) { print $manifest "monotonic_clock/$_" unless /^\./ }