RFR: JDK-8194141: Remove JDK9Wrappers

[Jonathan Gibbons]

Please review this code to remove a "temporary" class from javac, to 
provide reflective access to JDK 9 API, so that javac itself could be 
built with JDK 8.  This temporary class is no longer required, now that 
the boot JDK for JDK 10 onwards is JDK 9.

This is primarily about replacing the use of a javac internal class with 
the underlying direct API calls. However, a minor change to the autoconf 
spec is also required, to grant compile-time access to some internal JDK 
API. Some comments from the jdk.compiler module-info are also updated.

The fix is proposed for JDK 11.

JBS: https://bugs.openjdk.java.net/browse/JDK-8194141
Webrev: http://cr.openjdk.java.net/~jjg/8194141/webrev.00

-- Jon