The alternative source (alt-src) mechanism (altsrc.make) was introduced to allow alternative versions of common hotspot source files to be used in place of the originals when doing a build, or to find additional source files. This works fine when when you want to build using the alt-src and the alt-src location exists; and it works fine if you don't want to build with the alt-src and the alt-src location does not exist. But it doesn't work if you don't want to build with the alt-src but the alt-src location does exist - in this case you have to remove or rename the alt-src location so that it is not found.

An OpenJDK build (OPENJDK==true) is by definition a build that does not use the alt-src location. So the proposal is that for OpenJDK builds the alt-src mechanism will always be disabled.