RFR: Improve and modernize the makefile

Mon Mar 15 16:27:18 UTC 2021

On Mon, 15 Mar 2021 16:22:49 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> A bunch of fixes to the make file, to use more modern/robust syntax, and to keep intermediate build results.
> 
> This is a prerequisite for any further changes to the make file.

Note that with this change, the build result end up in `build/dist`, rather than `build` directly. Deployment scripts will likely need adaption to this change. 

The new directory `build/support` contains intermediate results that are needed by the build.

-------------

PR: https://git.openjdk.java.net/guide/pull/46