RFR: 8351151: Clean up x86 template interpreter after 32-bit x86 removal

[Coleen Phillimore]

On Wed, 26 Mar 2025 11:51:22 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> x86 template interpreter carries `_LP64`-predicated code blocks that were supporting 32-bit x86. With that port gone, we can clean up the x86 template interpreter. I have checked no superfluous `LP64`, `AMD64`, `IA32` defines are left in affected files.
> 
> Where obvious, I inlined `r15_thread` and `c_arg*`. Left the uses that assign these args to symbolic locals that have meaningful names.
> 
> `verify_FPU` is also no-op now, removed that. There are related cleanups in compilers and runtime we need to do first, before we fully remove `VerifyFPU` flag. This change fans out a little to other platform template interpreters to remove `verify_FPU` as well.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `tier1`
>  - [x] Linux x86_64 server fastdebug, `all`

Fred and I chatted about the r15_thread variable too, but agreed that this can be done incrementally later.

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PR Comment: https://git.openjdk.org/jdk/pull/24251#issuecomment-2757680713