Use File::PATH_SEPARATOR since we use it everywhere else

Library/ENV/4.3/xcrun

@@ -34,9 +34,7 @@ try `/usr/bin/xcrun --find #{arg0} 2>/dev/null`.chomp
 
 # xcrun won't always be able to find Homebrew's apple-gcc42,
 # even when it's in the PATH
-ENV['PATH'].split(':').each do |p|
-  try "#{p}/#{arg0}"
-end
+ENV["PATH"].split(File::PATH_SEPARATOR).each { |p| try File.join(p, arg0) }
 
 abort <<-EOS
 Your Xcode and or CLT are mis-configured. Try some or all of the following: