RFR: Improve and modernize the makefile [v2]

Tue Mar 16 14:13:20 UTC 2021

On Mon, 15 Mar 2021 19:57:27 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.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Additional improvements for reusability and debuggability

Looks good!

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Marked as reviewed by jwilhelm (Lead).

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