[riscv-port-jdk11u:riscv-port] RFR: 8291893: riscv: remove fence.i used in user space

[Ludovic Henry]

On Tue, 26 Mar 2024 08:35:05 GMT, Gui Cao <gcao at openjdk.org> wrote:

> Please help review this backport to riscv-port-jdk11u.
> Backport of [JDK-8291893](https://bugs.openjdk.org/browse/JDK-8291893)
> 
> In addition to the backport [8291947](https://bugs.openjdk.org/browse/JDK-8291947), we can use __builtin__clear_cache instead of icache_flush. 
> 
> Testing:
> 
> - [x] Run tier1-3 tests on SOPHON SG2042 (release)

Let's make sure we backport https://github.com/openjdk/jdk/commit/faf1b822d03b726413d77a2b247dfbbf4db7d57e as well as it's a fix for the commit you're backporting here.

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PR Comment: https://git.openjdk.org/riscv-port-jdk11u/pull/16#issuecomment-2020931991