https://bugs.gentoo.org/925072
https://github.com/OSGeo/gdal/pull/12771
https://github.com/OSGeo/gdal/commit/68a6868877f3dc661f1e843b0bfc290a4b9ec3ed

From 68a6868877f3dc661f1e843b0bfc290a4b9ec3ed Mon Sep 17 00:00:00 2001
From: Alfred Wingate <parona@protonmail.com>
Date: Tue, 22 Jul 2025 00:41:59 +0300
Subject: [PATCH] CMake: fix checks for CMAKE_SYSTEM_PROCESSOR on non Windows
 platforms

Linux and macOS match (x86|AMD64) due to a partial match on x86_64.

On Windows the valid values are AMD64/IA64/x86/ARM64
For Linux and macOS the output from uname -m is used instead.

macOS and Linux x86 -> i386/i486/i586/i686
(i386 and i486 irrelevent for SIMD)
macOS and Linux amd64 ->  x86_64
macOS and Linux arm ->  armv[567]
macos arm64 -> arm64
Linux arm64 ->  aarch64

https://cmake.org/cmake/help/latest/variable/CMAKE_SYSTEM_PROCESSOR.html
https://cmake.org/cmake/help/latest/variable/CMAKE_HOST_SYSTEM_PROCESSOR.html

A better defined variable in the future could be CMAKE_CXX_COMPILER_ARCHITECTURE_ID,
but values for Apple and UNIX platforms are new for the unreleased cmake-4.1.

https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER_ARCHITECTURE_ID.html

Bug: https://bugs.gentoo.org/925072
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -48,7 +48,7 @@ endif()
 include(Ccache)
 
 #
-if ("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(x86|AMD64)")
+if ("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(i586|i686|x86|AMD64)")
   check_compiler_machine_option(flag SSE)
   if (NOT ${flag} STREQUAL "")
     set(HAVE_SSE_AT_COMPILE_TIME 1)
--- a/cmake/helpers/CheckCompilerMachineOption.cmake
+++ b/cmake/helpers/CheckCompilerMachineOption.cmake
@@ -31,7 +31,7 @@ function(check_compiler_machine_option outvar feature)
   endmacro()
 
   set(_FLAGS)
-  if("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(x86|AMD64)")
+  if("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(i586|i686|x86|AMD64)")
     if(MSVC AND (${feature} MATCHES "SSE"))
       # SSE2 and SSE are default on
       set(_FLAGS " ")
@@ -100,7 +100,7 @@ function(check_compiler_machine_option outvar feature)
         endif()
       endif()
     endif()
-  elseif("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(ARM|aarch64)")
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(arm|ARM|aarch64)")
     if(MSVC)
       # TODO implement me
     elseif(CMAKE_CXX_COMPILER MATCHES "/(icpc|icc)$") # ICC (on Linux)