generated sources and make

[Maurizio Cimadamore]

Hi,
I was playing with the script for IntelliJ project generation, and I 
noted that make does not report generated source roots (e.g. those under 
support/gensrc) _unless_ such folders exist in the file system.

This is a bit of a let down - normally one would create the IJ project 
on an empty (but configured) OpenJDK repo - and if you do that, right 
now there will be missing source roots.

If you call 'make gensrc', the sources will be picked up by the 
script/makefiles, but that is a lengthy target to call, as it seems to 
build all the interim tools and java.base.

Would it be possible to correct this behavior, and to have the results 
of FindModuleSrcDirs _not_ depend on what has already been built?

Cheers
Maurizio