RFR: 8309228: Clarify EXPERIMENTAL flags comment in hotspot/share/runtime/globals.hpp

[David Holmes]

Please review this trivial update to  the comments in globals.hpp regarding the definition of EXPERIMENTAL flags.

Thanks.

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

Commit messages:
 - 8309228: Clarify EXPERIMENTAL flags comment in hotspot/share/runtime/globals.hpp

Changes: https://git.openjdk.org/jdk/pull/14550/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14550&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309228
  Stats: 6 lines in 1 file changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/14550.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14550/head:pull/14550

PR: https://git.openjdk.org/jdk/pull/14550