Index: cmake/Modules/CompilerRTDarwinUtils.cmake
===================================================================
--- cmake/Modules/CompilerRTDarwinUtils.cmake
+++ cmake/Modules/CompilerRTDarwinUtils.cmake
@@ -273,7 +273,7 @@
                       ../profile/InstrProfilingPlatformDarwin
                       ../profile/InstrProfilingWriter)
   foreach (os ${ARGN})
-    list_intersect(DARWIN_BUILTIN_ARCHS DARWIN_${os}_ARCHS BUILTIN_SUPPORTED_ARCH)
+    list_intersect(DARWIN_BUILTIN_ARCHS DARWIN_${os}_BUILTIN_ARCHS BUILTIN_SUPPORTED_ARCH)
     foreach (arch ${DARWIN_BUILTIN_ARCHS})
       darwin_find_excluded_builtins_list(${arch}_${os}_EXCLUDED_BUILTINS
                               OS ${os}
Index: cmake/builtin-config-ix.cmake
===================================================================
--- cmake/builtin-config-ix.cmake
+++ cmake/builtin-config-ix.cmake
@@ -62,6 +62,7 @@
   set(DARWIN_osx_BUILTIN_MIN_VER 10.5)
   set(DARWIN_osx_BUILTIN_MIN_VER_FLAG
       -mmacosx-version-min=${DARWIN_osx_BUILTIN_MIN_VER})
+  set(DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
 
   if(COMPILER_RT_ENABLE_IOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)
@@ -69,6 +70,8 @@
     set(DARWIN_ios_BUILTIN_MIN_VER 6.0)
     set(DARWIN_ios_BUILTIN_MIN_VER_FLAG
       ${DARWIN_ios_MIN_VER_FLAG}=${DARWIN_ios_BUILTIN_MIN_VER})
+    set(DARWIN_ios_BUILTIN_ALL_POSSIBLE_ARCHS ${ARM64} ${ARM32})
+    set(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
   endif()
   if(COMPILER_RT_ENABLE_WATCHOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS watchos)
@@ -76,6 +79,8 @@
     set(DARWIN_watchos_BUILTIN_MIN_VER 2.0)
     set(DARWIN_watchos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_watchos_MIN_VER_FLAG}=${DARWIN_watchos_BUILTIN_MIN_VER})
+    set(DARWIN_watchos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 armv7k)
+    set(DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86})
   endif()
   if(COMPILER_RT_ENABLE_TVOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS tvos)
@@ -83,6 +88,8 @@
     set(DARWIN_tvos_BUILTIN_MIN_VER 9.0)
     set(DARWIN_tvos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_tvos_MIN_VER_FLAG}=${DARWIN_tvos_BUILTIN_MIN_VER})
+    set(DARWIN_tvos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 arm64)
+    set(DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
   endif()
 
   set(BUILTIN_SUPPORTED_OS osx)
@@ -90,15 +97,16 @@
   # We're setting the flag manually for each target OS
   set(CMAKE_OSX_DEPLOYMENT_TARGET "")
 
-  if(NOT DARWIN_osx_ARCHS)
-    set(DARWIN_osx_ARCHS i386 x86_64 x86_64h)
-  endif()
-
-  set(DARWIN_sim_ARCHS i386 x86_64)
-  set(DARWIN_device_ARCHS armv7 armv7s armv7k arm64)
-
-  message(STATUS "OSX supported arches: ${DARWIN_osx_ARCHS}")
-  foreach(arch ${DARWIN_osx_ARCHS})
+  # NOTE: We deliberately avoid using `DARWIN_<os>_ARCHS` here because that is
+  # used by `config-ix.cmake` in the context of building the rest of
+  # compiler-rt where the global `${TEST_COMPILE_ONLY}` (used by
+  # `darwin_test_archs()`) has a different value.
+  darwin_test_archs(osx
+    DARWIN_osx_BUILTIN_ARCHS
+    ${DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS}
+  )
+  message(STATUS "OSX supported builtin arches: ${DARWIN_osx_BUILTIN_ARCHS}")
+  foreach(arch ${DARWIN_osx_BUILTIN_ARCHS})
     list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
     set(CAN_TARGET_${arch} 1)
   endforeach()
@@ -112,38 +120,30 @@
 
       set(DARWIN_${platform}sim_SKIP_CC_KEXT On)
 
-      set(test_arches ${DARWIN_sim_ARCHS})
-      if(DARWIN_${platform}sim_ARCHS)
-        set(test_arches DARWIN_${platform}sim_ARCHS)
-      endif()
-
       darwin_test_archs(${platform}sim
-        DARWIN_${platform}sim_ARCHS
-        ${test_arches})
-      message(STATUS "${platform} Simulator supported builtin arches: ${DARWIN_${platform}sim_ARCHS}")
-      if(DARWIN_${platform}sim_ARCHS)
+        DARWIN_${platform}sim_BUILTIN_ARCHS
+        ${DARWIN_${platform}sim_BUILTIN_ALL_POSSIBLE_ARCHS}
+      )
+      message(STATUS "${platform} Simulator supported builtin arches: ${DARWIN_${platform}sim_BUILTIN_ARCHS}")
+      if(DARWIN_${platform}sim_BUILTIN_ARCHS)
         list(APPEND BUILTIN_SUPPORTED_OS ${platform}sim)
       endif()
-      foreach(arch ${DARWIN_${platform}sim_ARCHS})
+      foreach(arch ${DARWIN_${platform}sim_BUILTIN_ARCHS})
         list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
         set(CAN_TARGET_${arch} 1)
       endforeach()
     endif()
 
     if(DARWIN_${platform}_SYSROOT)
-      set(test_arches ${DARWIN_device_ARCHS})
-      if(DARWIN_${platform}_ARCHS)
-        set(test_arches DARWIN_${platform}_ARCHS)
-      endif()
-
       darwin_test_archs(${platform}
-        DARWIN_${platform}_ARCHS
-        ${test_arches})
-      message(STATUS "${platform} supported builtin arches: ${DARWIN_${platform}_ARCHS}")
-      if(DARWIN_${platform}_ARCHS)
+        DARWIN_${platform}_BUILTIN_ARCHS
+        ${DARWIN_${platform}_BUILTIN_ALL_POSSIBLE_ARCHS}
+      )
+      message(STATUS "${platform} supported builtin arches: ${DARWIN_${platform}_BUILTIN_ARCHS}")
+      if(DARWIN_${platform}_BUILTIN_ARCHS)
         list(APPEND BUILTIN_SUPPORTED_OS ${platform})
       endif()
-      foreach(arch ${DARWIN_${platform}_ARCHS})
+      foreach(arch ${DARWIN_${platform}_BUILTIN_ARCHS})
         list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
         set(CAN_TARGET_${arch} 1)
       endforeach()