Index: llvm/trunk/cmake/config-ix.cmake
===================================================================
--- llvm/trunk/cmake/config-ix.cmake
+++ llvm/trunk/cmake/config-ix.cmake
@@ -554,6 +554,22 @@
 set(LLVM_BINUTILS_INCDIR "" CACHE PATH
 	"PATH to binutils/include containing plugin-api.h for gold plugin.")
 
+if(CMAKE_GENERATOR STREQUAL "Ninja")
+  include(CMakeNInjaFindMake)
+  if(CMAKE_MAKE_PROGRAM)
+    execute_process(COMMAND ${CMAKE_MAKE_PROGRAM} --version
+      OUTPUT_VARIABLE NINJA_VERSION
+      OUTPUT_STRIP_TRAILING_WHITESPACE)
+    set(NINJA_VERSION ${NINJA_VERSION} CACHE STRING "Ninja version number" FORCE)
+  endif()
+endif()
+
+if(CMAKE_GENERATOR STREQUAL "Ninja" AND
+    NINJA_VERSION VERSION_GREATER_EQUAL "1.9.0" AND
+    CMAKE_HOST_APPLE AND CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER "15.6.0")
+  set(LLVM_TOUCH_STATIC_LIBRARIES ON)
+endif()
+
 if(CMAKE_HOST_APPLE AND APPLE)
   if(NOT CMAKE_XCRUN)
     find_program(CMAKE_XCRUN NAMES xcrun)
Index: llvm/trunk/cmake/modules/AddLLVM.cmake
===================================================================
--- llvm/trunk/cmake/modules/AddLLVM.cmake
+++ llvm/trunk/cmake/modules/AddLLVM.cmake
@@ -596,6 +596,18 @@
     llvm_externalize_debuginfo(${name})
     llvm_codesign(${name} ENTITLEMENTS ${ARG_ENTITLEMENTS})
   endif()
+  # clang and newer versions of ninja use high-resolutions timestamps,
+  # but older versions of libtool on Darwin don't, so the archive will
+  # often get an older timestamp than the last object that was added
+  # or updated.  To fix this, we add a custom command to touch archive
+  # after it's been built so that ninja won't rebuild it unnecessarily
+  # the next time it's run.
+  if(ARG_STATIC AND LLVM_TOUCH_STATIC_LIBRARIES)
+    add_custom_command(TARGET ${name}
+      POST_BUILD
+      COMMAND touch ${LLVM_LIBRARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${name}${CMAKE_STATIC_LIBRARY_SUFFIX}
+      )
+  endif()
 endfunction()
 
 function(add_llvm_install_targets target)