RFR: JDK-8314056 Remove runtime platform check from frem/drem [v3]

[Jatin Bhateja]

On Wed, 23 Aug 2023 23:17:00 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

>> Remove platform check and move code to stubGenerator.  This fix increases performance by ~4.5%.
>> 
>> UPDATE: Subsequent commits increase performance gain to ~2x for AVX2, with no significant change to AVX512.
>> 
>> Tested tier1.
>
> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   mxcsr fix; address review comments

Marked as reviewed by jbhateja (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/15210#pullrequestreview-1601725307