RFR: 8291947: riscv: fail to build after JDK-8290840

[Fei Yang]

On Fri, 5 Aug 2022 03:27:41 GMT, Yadong Wang <yadongwang at openjdk.org> wrote:

> [JDK-8290840](https://bugs.openjdk.org/browse/JDK-8290840) moved icache_flush from os_linux_riscv.cpp to icache_riscv.cpp, and we got 2 icache_flush there, and then caused a compilation error of "overloaded function with no contextual type information" in generate_icache_flush, which simply used the function name as a function address.
> 
> We put icache_flush in os files because it was just a linux implementation, and we saw some test failures on Hifive Unleashed when using the "portable" version of __builtin__clear_cache provided by compilers about 2 years ago. The problem doesn't exist anymore, so we can revert to the previous implementation of just using the builtin clear cache function.
> 
> Tier1 of hotspot and jdk passed on unmatched.

Marked as reviewed by fyang (Reviewer).

Verified that riscv port can build with this fix. Looks good.

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

PR: https://git.openjdk.org/jdk/pull/9763