RFR: 8153416 unexport javah from jdk.compiler module

[Jonathan Gibbons]

This patch removes com.sun.tools.javah from the set of packages exported 
from jdk.compiler, and updates the @modules tag of tests that use the 
entry point, either directly, or via ToolBox JavahTask.

JBS: https://bugs.openjdk.java.net/browse/JDK-8153416
Webrev: http://cr.openjdk.java.net/~jjg/8153416/webrev.00

-- Jon