Improve the specification of `Linker.Option.firstVariadicArg`, by specifying more clearly which index values are valid.
------------- Commit messages: - improve firstVariadicArg doc Changes: https://git.openjdk.org/jdk/pull/14565/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14565&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8310405 Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/14565.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/14565/head:pull/14565 PR: https://git.openjdk.org/jdk/pull/14565
