The new Hotspot Build System

[Erik Joelsson]

The first phase of the new Hotspot Build System (JEP 284) has now been 
pushed to jdk9/hs-rt. During a transition period, both the old and new 
build system will co-exist and you can pick the one you want using the 
configure option "--disable-new-hotspot-build". The new system is the 
default while the old is there as a backup in case your particular work 
flow broke in the new system. If you have any trouble, don't hesitate to 
contact me or file an issue.

The goal is to push the second phase, where the old system is removed, 
and the new moves from hotspot/makefiles to hotspot/make, as soon as 
possible. If no blocking issues are raised, I will propose to push that 
change in one weeks time from today. This is of course negotiable.

The change to the new build system also means that the infra team now 
assumes responsibility for the Hotspot makefiles. This means that all 
changes that touch makefiles should include build-dev in the review. 
This is especially important during the transition period so that we can 
ensure that both build systems are kept in sync.

The user of the build shouldn't notice much of a difference. If you 
build from the top level, "make hotspot" will still do the same thing. 
The new build does not support building from the hotspot repo. Debug 
levels are controlled through the same configure parameters as before. 
There is one new configure parameter, --with-jvm-features, that can be 
used to create specialized builds with non standard combinations of jvm 
options, especially in conjunction with the new jvm variant "custom". 
See the configure help output for more details. There is a new way of 
generating Visual Studio projects using the top level target 
"hotspot-ide-project", which replaces the old script.

/Erik