Require both CFLAGS and LDFLAGS to be empty in order to skip.

[basking2]

In Fedora 20 I observed that installing ruby-lua-0.4.0 succeeded, but the compiled lua.so did not know to dynamically load the lua library. It was missing the -llua flag.

examining extconf.rb showed the when falling back to using pkg-config a result is skipped if both cf and ldf are empty. In Fedora 20 CFLAGS is empty, and that is not an error, while LDFLAGS has the missing libraries.

I thought the easiest change would be to make the or and and as you can see in the diff. If pkg-config has nothing to add to the compilation, try again. If it adds anything, assume it is correct and complete.

[shagabutdinov]

Confirm, experienced same problem, this will fix the issue.

Also it'll be good to raise "lua not found" message if no lua found in section "["lua", "lua5.1", "lua5.2"].any?"; like this:

  found = ["lua", "lua5.1", "lua5.2"].any? do |l|
    ldf = `#{ex} --libs #{l}`.chomp
    cf = `#{ex} --cflags #{l}`.chomp
    next false if ldf.empty? and cf.empty?

    $LDFLAGS << " #{ldf}"
    $CFLAGS  << " #{cf}"
    true
  end

  if !found
    crash_lua_not_found()
  end