Excessive rebuilds of modules

[Ioi Lam]

If I change a line of code in the java.base module, every Java module is 
rebuilt. However, my change does not change any of the APIs or the 
module info.

I think this means none of the other modules would be affected. If this 
is true, maybe we can modify the build system to check this and avoid 
the excessive rebuilds?

Thanks
- Ioi