cmake: move CMAKE_OSX_ARCHITECTURES out of the stdenv

This was initially introduced in 92188d9d17,
not clear how relevant this still is but i686 isn't supported anymore so
disable it explicitly.

pkgs/development/tools/build-managers/cmake/setup-hook.sh

@@ -50,6 +50,9 @@ cmakeConfigurePhase() {
     # because we usually do not package the framework
     cmakeFlags="-DCMAKE_FIND_FRAMEWORK=last $cmakeFlags"
 
+    # on macOS i686 was only relevant for 10.5 or earlier.
+    cmakeFlags="-DCMAKE_OSX_ARCHITECTURES=x86_64 $cmakeFlags"
+
     # we never want to use the global macOS SDK
     cmakeFlags="-DCMAKE_OSX_SYSROOT= $cmakeFlags"
 

pkgs/stdenv/darwin/default.nix

@@ -34,7 +34,6 @@ in rec {
     export NIX_ENFORCE_NO_NATIVE=''${NIX_ENFORCE_NO_NATIVE-1}
     export NIX_ENFORCE_PURITY=''${NIX_ENFORCE_PURITY-1}
     export NIX_IGNORE_LD_THROUGH_GCC=1
-    export CMAKE_OSX_ARCHITECTURES=x86_64
     export SDKROOT=
 
     # Ensure consistent LC_VERSION_MIN_MACOSX and remove LC_UUID.