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

[Joachim Kern]

On Wed, 10 Apr 2024 22:14:33 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> That build failure in shared code does not happen with Xcode clang, gcc, or
>> Visual Studio, even though none of them appear to have a relevant define or
>> include. So the clang variant being used for AIX is different from the Xcode
>> clang variant (and maybe others) in its treatment of alloca. Weird!
>> 
>> I can also live with either the macro or the includes where needed.  I dislike
>> conditionally adding the include in globalDefinitions_gcc.hpp.
>
> Should also remove the `#pragma alloca` in os_aix.cpp.

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?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18536#discussion_r1566988309