improve cross-platform git check in gemspec

[ci skip]

will_paginate.gemspec

@@ -1,4 +1,5 @@
 # encoding: utf-8
+require 'rbconfig'
 require File.expand_path('../lib/will_paginate/version', __FILE__)
 
 Gem::Specification.new do |s|
@@ -16,5 +17,13 @@ Gem::Specification.new do |s|
   s.extra_rdoc_files = ['README.md', 'LICENSE']
 
   s.files = Dir['Rakefile', '{bin,lib,test,spec}/**/*', 'README*', 'LICENSE*']
-  s.files &= `git ls-files -z`.split("\0") if `type -t git 2>/dev/null || which git 2>/dev/null` && $?.success?
+
+  # include only files in version control
+  git_dir = File.expand_path('../.git', __FILE__)
+  void = defined?(File::NULL) ? File::NULL :
+    RbConfig::CONFIG['host_os'] =~ /msdos|mswin|djgpp|mingw/ ? 'NUL' : '/dev/null'
+
+  if File.directory?(git_dir) and system "git --version >>#{void} 2>&1"
+    s.files &= `git --git-dir='#{git_dir}' ls-files -z`.split("\0") 
+  end
 end