RFR: 8171508: Remove -Dsun.java.launcher.is_altjvm option [v5]

[Thomas Stuefe]

On Mon, 7 Apr 2025 17:56:31 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

>> The `-Dsun.java.launcher.is_altjvm` option is only used in the gtest launcher and has no relationship with the similarly named `-XXaltjvm` option. The gtest launcher also sets the `-XX:+ExecutingUnitTests` option. This RFE involves removing the `-Dsun.java.launcher.is_altjvm` option, capturing the `-XX:+ExecutingUnitTests` option in Arguments::process_sun_java_launcher_properties() so that the os::jvm_path() can check if the option is set before using JAVA_HOME setting.
>> 
>> Passed tiers 1 - 3 testing.
>
> Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:
> 
>   @dholmes-ora comments

Are the Posix variants all identical? If yes, can we move this to os::posix.cpp? If not, what are the differences?

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PR Review: https://git.openjdk.org/jdk/pull/24310#pullrequestreview-2748768608