RFR: JDK-8157511: JDK-8157348 broke gensrc of module infos with extra provides

[Erik Joelsson]

Another fallout from JDK-8157511. We don't just modify exports, but also 
provides and those do not deal with packages, so the new condition 
disables all of them. This fix makes the handling of exports and 
provides very explicit. That's probably a good thing since we only 
support exports and provides in the module-info.extra files. I have 
verified on a mac that the missing AppleProvider is now present.

Bug: https://bugs.openjdk.java.net/browse/JDK-8157511
Webrev: http://cr.openjdk.java.net/~erikj/8157511/webrev.top.01/

/Erik