Merge pull request #2885 from apple/cmake-Configure-policy-CMP0116

[cmake] Configure policy CMP0116

Author: kastiglione

llvm/CMakeLists.txt

@@ -15,6 +15,12 @@ if(POLICY CMP0077)
   cmake_policy(SET CMP0077 NEW)
 endif()
 
+# CMP0116: Ninja generators transform `DEPFILE`s from `add_custom_command()`
+# New in CMake 3.20. https://cmake.org/cmake/help/latest/policy/CMP0116.html
+if(POLICY CMP0116)
+  cmake_policy(SET CMP0116 OLD)
+endif()
+
 if(NOT DEFINED LLVM_VERSION_MAJOR)
   set(LLVM_VERSION_MAJOR 12)
 endif()