RFR: 8351323: Parameterize compiler and linker flags for iconv

[Erik Joelsson]

On Tue, 11 Mar 2025 19:22:34 GMT, snake66 <duke at openjdk.org> wrote:

> Allows for future support for platforms that require different flags for libiconv support.
> 
> Sponsored-by: The FreeBSD Foundation

I think this looks ok, but please wait for Magnus to have a look too.

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Marked as reviewed by erikj (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23995#pullrequestreview-2675894294