Index: compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
===================================================================
--- compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
+++ compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
@@ -298,6 +298,14 @@
          -target "${LIB_ARCH}-apple-${base_os}${DARWIN_${LIBOS}_BUILTIN_MIN_VER}-simulator")
   endif()
 
+  if ("${COMPILER_RT_ENABLE_MACCATALYST}" AND
+      "${LIB_OS}" MATCHES "^osx$")
+    # Build the macOS builtins with Mac Catalyst support.
+    list(APPEND builtin_cflags
+      -target ${LIB_ARCH}-apple-macos${DARWIN_osx_BUILTIN_MIN_VER}
+      -darwin-target-variant ${LIB_ARCH}-apple-ios13.0-macabi)
+  endif()
+
   set_target_compile_flags(${libname}
     ${sysroot_flag}
     ${DARWIN_${LIB_OS}_BUILTIN_MIN_VER_FLAG}
Index: compiler-rt/cmake/base-config-ix.cmake
===================================================================
--- compiler-rt/cmake/base-config-ix.cmake
+++ compiler-rt/cmake/base-config-ix.cmake
@@ -3,6 +3,7 @@
 # .o files. This is particularly useful in producing larger, more complex
 # runtime libraries.
 
+include(BuiltinTests)
 include(CheckIncludeFile)
 include(CheckCXXSourceCompiles)
 include(GNUInstallDirs)
@@ -138,6 +139,12 @@
     set(OSX_SYSROOT_FLAG "")
   endif()
 
+  try_compile_only(COMPILER_RT_HAS_DARWIN_TARGET_VARIANT_FLAG
+                   FLAGS
+                   "-target" "x86_64-apple-macos10.15"
+                   "-darwin-target-variant" "x86_64-apple-ios13.1-macabi"
+                   "-Werror")
+  option(COMPILER_RT_ENABLE_MACCATALYST "Enable building for Mac Catalyst" ${COMPILER_RT_HAS_DARWIN_TARGET_VARIANT_FLAG})
   option(COMPILER_RT_ENABLE_IOS "Enable building for iOS" On)
   option(COMPILER_RT_ENABLE_WATCHOS "Enable building for watchOS - Experimental" Off)
   option(COMPILER_RT_ENABLE_TVOS "Enable building for tvOS - Experimental" Off)