RFR JDK-8167442: Langtools ant build not working after addition of -Xlint:exports

[Jan Lahoda]

Bug:
https://bugs.openjdk.java.net/browse/JDK-8167442

Proposed solution is to disable the exports lint when compiling the 
langtools sources (the lint is disabled for the jdk.jshell module when 
building using the make buildsystem).

Webrev:
http://cr.openjdk.java.net/~jlahoda/8167442/webrev.00/

Any feedback is welcome.

Thanks,
     Jan