RFR: JDK-8282532: Allow explicitly setting build platform alongside --openjdk-target [v4]

[Julian Waters]

On Thu, 3 Mar 2022 15:54:44 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> Would it be better if I changed that to say the flags are misleading, or if I reverted it back to legacy in that case? (Since that seems to be the primary concern with using them)
>
> As the build documentation says, the standard autoconf tripled was created for building Canadian cross compilers (i.e. cross-compiling a cross-compiler). This means that they use "host" for what we call "target", and they use "target" for something that is not relevant for us. This caused a lot of confusion early on when OpenJDK started using autoconf.
> 
> If you know what you are doing, there's nothing inherently *wrong* with using the autoconf triplet. It's just confusing, due to the name clash of "target".
> 
> If you think this is not clear enough from the documenation and need to add something to the warnings printed by the configure wrapper, sure, go ahead and add a line about how this can be confusing. 
> 
> But it is not unsafe.

Alright, will change accordingly, thanks for the review

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PR: https://git.openjdk.java.net/jdk/pull/7656