RFR: 8246494: introduce vm.flagless at-requires property

[Igor Ignatyev]

resurrecting old [RFR](https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-June/041981.html):

> Hi all,
> 
> could you please review the patch which introduces a new @requires property to filter out the tests which ignore externally provided JVM flags?
> 
> the idea behind this patch is to have a way to clearly mark tests which ignore flags, so 
> a) it's obvious that they don't execute a flag-guarded code/feature, and extra care should be taken to use them to verify any flag-guarded changed;
> b) they can be easily excluded from runs w/ flags.
> 
> @requires and VMProps allows us to achieve both, so it's been decided to add a new property `vm.flagless`. `vm.flagless` is set to false if there are any XX flags other than `-XX:MaxRAMPercentage` and `-XX:CreateCoredumpOnCrash` (which are known to be set almost always) or any X flags other `-Xmixed`; in other words any tests w/ `@requires vm.flagless` will be excluded from runs w/ any other X / XX flags passed via `-vmoption` / `-javaoption`. in rare cases, when one still wants to run the tests marked by `vm.flagless`  w/ external flags, `vm.flagless` can be forcefully set to true by setting any value to `TEST_VM_FLAGLESS` env. variable.
> 
> this patch adds necessary common changes and marks common tests, namely Scimark, GTestWrapper and TestNativeProcessBuilder. Component-specific tests will be marked separately by the corresponding subtasks of 8151707[1].
> 
> please note, the patch depends on CODETOOLS-7902336[2], which will be included in the next jtreg version, so this patch is to be integrated only after jtreg5.1 is promoted and we switch to use it by 8246387[3].
> 
> JBS: https://bugs.openjdk.java.net/browse/JDK-8246494
> webrev: http://cr.openjdk.java.net/~iignatyev//8246494/webrev.00
> testing: marked tests w/ different XX and X flags w/ and w/o TEST_VM_FLAGLESS env. var, and w/o any flags
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8151707
> [2] https://bugs.openjdk.java.net/browse/CODETOOLS-7902336
> [3] https://bugs.openjdk.java.net/browse/JDK-8246387
> 

after offline discussion with @pliden, it has been decided to reduce the scope of [8246499](https://bugs.openjdk.java.net/browse/JDK-8246499) and not mark the tests that use `UseXGC` flags for selection, e.g. `test/hotspot/jtreg/gc/z/TestSmallHeap.java`.

Thanks,
-- Igor

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

Commit messages:
 - update copyright year
 - 8246494: introduce vm.flagless at-requires property

Changes: https://git.openjdk.java.net/jdk/pull/2800/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2800&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8246494
  Stats: 81 lines in 6 files changed: 75 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2800.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2800/head:pull/2800

PR: https://git.openjdk.java.net/jdk/pull/2800