Request for review: 7036525 Disable alternative source mechanism for OPENJDK builds

[David Holmes]

Okay now that my brain is functioning again lets see if it is third-time 
lucky:

http://cr.openjdk.java.net/~dholmes/7036525/webrev.2/

This reverts things back to my original webrev where we set 
HS_ALT_SRC_REL to NO_SUCH_PATH. It has to be a non-existent path 
otherwise it will appear in the generated definitions for Src_Dirs_I and 
Src_Dirs_V.

The user can override this by setting OPENJDK=true and 
HS_ALT_SRC_REL=<whatever> as variables on the make invocation eg:

gmake OPENJDK=true HS_ALT_SRC_REL=/my/dist/src product1

Thanks,
David