From 89741958e870659fbe8a1dcfb6f52ce012424d9a Mon Sep 17 00:00:00 2001
From: Viktor Szakats <commit@vsz.me>
Date: Sun, 30 Nov 2025 17:27:52 +0100
Subject: [PATCH] cmake: use `AIX` built-in variable (with CMake 4.0+)

Also keep the old method for compatibility with CMake <4.0.

Ref: https://cmake.org/cmake/help/v4.0/variable/AIX.html

Closes #21134
---
 CMake/OtherTests.cmake | 2 +-
 CMakeLists.txt         | 2 +-
 lib/CMakeLists.txt     | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/CMake/OtherTests.cmake b/CMake/OtherTests.cmake
index 650a42d8bd..6619f3ab3e 100644
--- a/CMake/OtherTests.cmake
+++ b/CMake/OtherTests.cmake
@@ -78,7 +78,7 @@ if(WIN32)
 elseif(NOT HAVE_GETADDRINFO)
   set(HAVE_GETADDRINFO_THREADSAFE FALSE)
 elseif(APPLE OR
-       CMAKE_SYSTEM_NAME STREQUAL "AIX" OR
+       AIX OR CMAKE_SYSTEM_NAME STREQUAL "AIX" OR
        CMAKE_SYSTEM_NAME STREQUAL "FreeBSD" OR
        CMAKE_SYSTEM_NAME STREQUAL "HP-UX" OR
        CMAKE_SYSTEM_NAME STREQUAL "MidnightBSD" OR
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 06a21b1ce5..a0a4a016d6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -596,7 +596,7 @@ if((ENABLE_CURL_MANUAL OR BUILD_LIBCURL_DOCS) AND NOT Perl_FOUND)
 endif()
 
 # If we are on AIX, do the _ALL_SOURCE magic
-if(CMAKE_SYSTEM_NAME STREQUAL "AIX")
+if(AIX OR CMAKE_SYSTEM_NAME STREQUAL "AIX")
   set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS "_ALL_SOURCE")
 endif()
 
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 1b6f6b36ba..aae466c677 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -247,7 +247,7 @@ if(BUILD_SHARED_LIBS)
   if(CMAKE_DLL_NAME_WITH_SOVERSION OR
     CYGWIN OR
     APPLE OR
-    CMAKE_SYSTEM_NAME STREQUAL "AIX" OR
+    AIX OR CMAKE_SYSTEM_NAME STREQUAL "AIX" OR
     CMAKE_SYSTEM_NAME STREQUAL "Linux" OR
     CMAKE_SYSTEM_NAME STREQUAL "SunOS" OR
     CMAKE_SYSTEM_NAME STREQUAL "Haiku" OR