RFR: 8353192: C2: Clean up x86 backend after 32-bit x86 removal

[Vladimir Kozlov]

On Fri, 28 Mar 2025 17:09:19 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Piece-wise cleanup of C2 x86 backend. C2_MacroAssembler, x86.ad and related files are the target for this cleanup. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `all`
>  - [x] Linux x86_64 server fastdebug, `all` + `-XX:-TieredCompilation`

I looked on `adlc` code to make sure nothing left there and found check for `IA32`. This looks like another variable we set for 32-bit x86:  [platform.m4#L556](https://github.com/openjdk/jdk/blob/master/make/autoconf/platform.m4#L556)
I surprise to see `X32` too which we check in `os_linux.cpp`.

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

PR Comment: https://git.openjdk.org/jdk/pull/24300#issuecomment-2776475220