diff --git a/compiler-rt/cmake/builtin-config-ix.cmake b/compiler-rt/cmake/builtin-config-ix.cmake
--- a/compiler-rt/cmake/builtin-config-ix.cmake
+++ b/compiler-rt/cmake/builtin-config-ix.cmake
@@ -80,33 +80,41 @@
 
   # Get supported architecture from SDKSettings.
   function(sdk_has_arch_support sdk_path os arch has_support)
+    set(sdk_json "${sdk_path}/SDKSettings.json")
+    # We can switch to string(JSON) once our minimum CMake version is 3.19+.
     execute_process(COMMAND
-        /usr/libexec/PlistBuddy -c "Print :SupportedTargets:${os}:Archs" ${sdk_path}/SDKSettings.plist
-      OUTPUT_VARIABLE SDK_SUPPORTED_ARCHS
-      RESULT_VARIABLE PLIST_ERROR
+      "${Python3_EXECUTABLE}" -c
+      # `not in` so that our exit code is 0 (success) if the arch is found
+      "import json; exit('${arch}' not in json.load(open('${sdk_json}'))['SupportedTargets']['${os}']['Archs'])"
+      RESULT_VARIABLE ARCH_FIND_RESULT
       ERROR_QUIET)
-    if (PLIST_ERROR EQUAL 0 AND
-        SDK_SUPPORTED_ARCHS MATCHES " ${arch}\n")
-      message(STATUS "Found ${arch} support in ${sdk_path}/SDKSettings.plist")
+    if (ARCH_FIND_RESULT EQUAL 0)
+      message(STATUS "Found ${arch} support in ${sdk_json}")
       set("${has_support}" On PARENT_SCOPE)
     else()
-      message(STATUS "No ${arch} support in ${sdk_path}/SDKSettings.plist")
+      message(STATUS "No ${arch} support in ${sdk_json}")
       set("${has_support}" Off PARENT_SCOPE)
     endif()
   endfunction()
 
+  # Add support for arm64 if available in SDK.
+  function(add_arm64_if_supported sdk_path os archs_var)
+    set(local_archs ${${archs_var}})
+    foreach(arch ${ARM64})
+      sdk_has_arch_support(${sdk_path} ${os} ${arch} has_support)
+      if(has_support)
+        list(APPEND local_archs ${arch})
+      endif()
+    endforeach()
+    set(${archs_var} ${local_archs} PARENT_SCOPE)
+  endfunction()
+
   set(DARWIN_EMBEDDED_PLATFORMS)
   set(DARWIN_osx_BUILTIN_MIN_VER 10.5)
   set(DARWIN_osx_BUILTIN_MIN_VER_FLAG
       -mmacosx-version-min=${DARWIN_osx_BUILTIN_MIN_VER})
   set(DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-  # Add support for arm64 macOS if available in SDK.
-  foreach(arch ${ARM64})
-    sdk_has_arch_support(${DARWIN_osx_SYSROOT} macosx ${arch} MACOS_ARM_SUPPORT)
-    if (MACOS_ARM_SUPPORT)
-     list(APPEND DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${arch})
-    endif()
-  endforeach(arch)
+  add_arm64_if_supported(${DARWIN_osx_SYSROOT} macosx DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS)
 
   if(COMPILER_RT_ENABLE_IOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)
@@ -116,10 +124,7 @@
       ${DARWIN_ios_MIN_VER_FLAG}=${DARWIN_ios_BUILTIN_MIN_VER})
     set(DARWIN_ios_BUILTIN_ALL_POSSIBLE_ARCHS ${ARM64} ${ARM32})
     set(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-    find_darwin_sdk_version(iossim_sdk_version "iphonesimulator")
-    if ("${iossim_sdk_version}" VERSION_GREATER 14.0 OR "${iossim_sdk_version}" VERSION_EQUAL 14.0)
-      list(APPEND DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_iossim_SYSROOT} iphonesimulator DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
   if(COMPILER_RT_ENABLE_WATCHOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS watchos)
@@ -129,10 +134,7 @@
       ${DARWIN_watchos_MIN_VER_FLAG}=${DARWIN_watchos_BUILTIN_MIN_VER})
     set(DARWIN_watchos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 armv7k arm64_32)
     set(DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86})
-    find_darwin_sdk_version(watchossim_sdk_version "watchsimulator")
-    if ("${watchossim_sdk_version}" VERSION_GREATER 7.0 OR "${watchossim_sdk_version}" VERSION_EQUAL 7.0)
-      list(APPEND DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_watchossim_SYSROOT} watchsimulator DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
   if(COMPILER_RT_ENABLE_TVOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS tvos)
@@ -142,10 +144,7 @@
       ${DARWIN_tvos_MIN_VER_FLAG}=${DARWIN_tvos_BUILTIN_MIN_VER})
     set(DARWIN_tvos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 arm64)
     set(DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-    find_darwin_sdk_version(tvossim_sdk_version "appletvsimulator")
-    if ("${tvossim_sdk_version}" VERSION_GREATER 14.0 OR "${tvossim_sdk_version}" VERSION_EQUAL 14.0)
-      list(APPEND DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_tvossim_SYSROOT} appletvsimulator DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
 
   set(BUILTIN_SUPPORTED_OS osx)