Set explicitly the desired Darwin architecture for all CMake builds

This would be needed to compile on Apple Silicon, so that CMake does not
infer the wrong architecture when we want to build for Intel (see
https://gitlab.kitware.com/cmake/cmake/-/merge_requests/5291)

Addresses rdar://99587478

Author: edymtt

Utilities/build-script-helper.py

@@ -425,6 +425,7 @@ def build_using_cmake(args, toolchain_bin, build_dir, targets):
     swift_flags.append('-target %s' % target)
     if platform.system() == 'Darwin':
       base_cmake_flags.append('-DCMAKE_OSX_DEPLOYMENT_TARGET=%s' % macos_deployment_target)
+      base_cmake_flags.append('-DCMAKE_OSX_ARCHITECTURES=%s' % target.split('-')[0])
 
     # Target directory for build artifacts
     # If building for a local compiler build, use the build directory directly
@@ -469,8 +470,6 @@ def build_llbuild_using_cmake(args, target, swiftc_exec, build_dir, base_cmake_f
         '-DCMAKE_CXX_FLAGS=-target %s' % target,
         '-DLLBUILD_SUPPORT_BINDINGS:=Swift'
     ]
-  if platform.system() == 'Darwin':
-    flags.append('-DCMAKE_OSX_ARCHITECTURES=%s' % target.split('-')[0])
   llbuild_cmake_flags = base_cmake_flags + flags
   if args.sysroot:
     llbuild_cmake_flags.append('-DSQLite3_INCLUDE_DIR=%s/usr/include' % args.sysroot)