RFR: 8357119: Make Zero the default and only variant of HotSpot for iOS [v2]

[Magnus Ihse Bursie]

On Fri, 16 May 2025 08:58:37 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> Currently, the Zero variant of HotSpot must be manually selected for mobile to compile properly for iOS, since iOS does not allow writeable and executable sections. Since Zero is, to my knowledge, the only valid HotSpot variant for iOS, this default should be handled by the build rather than require the developer to have specific knowledge about iOS and the mobile fork. I also took the opportunity to explicitly disallow selecting other JVM variants at all for iOS, this can be rolled back if my assumption turns out to be incorrect. While here, also touch up the build docs a little.
>
> Julian Waters has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Touch up README.md

We can test for ifdefs by test compiling code, but it is not the most efficient way. Checking for `if [[ SYSROOT =~ .*Simulator.* ]]` seems simpler.

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

PR Comment: https://git.openjdk.org/mobile/pull/35#issuecomment-2887609608