RFR: 8329257: AIX: Switch HOTSPOT_TOOLCHAIN_TYPE from xlc to gcc [v3]

[Magnus Ihse Bursie]

On Tue, 16 Apr 2024 09:14:25 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> We can not use `#include <alloca.h>` in all files which use `alloca`, because windows does not know this header. Maybe we can use `#include <alloca.h>` unconditionally in globalDefinitions_gcc.hpp, if windows will never use this file. @kimbarrett What do you say?
>
> That was kind of where the discussion started, and which Kim did not like. If I read him correctly, his suggestion was instead to place:
> 
> #if defined(_AIX)
> #include <alloca.h>
> #endif
> 
> in the files where `alloca` is needed on AIX.

(If some of these files happen to be files which are not compiled on Windows, I assume it will not hurt to drop the ifdef guard, but then again, it can certainly be kept as well for consistency.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/18536#discussion_r1567027594