Fix build failure with cmake version bump

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@271582 91177308-0d34-0410-b5e6-96231b3b80d8

Author: david-xl

CMakeLists.txt

@@ -16,6 +16,16 @@ else()
 endif()
 
 cmake_minimum_required(VERSION 3.4.3)
+# FIXME:
+# The OLD behavior (pre 3.2) for this policy is to not set the value of the 
+# CMAKE_EXE_LINKER_FLAGS variable in the generated test project. The NEW behavior
+# for this policy is to set the value of the CMAKE_EXE_LINKER_FLAGS variable 
+# in the test project to the same as it is in the calling project. The new 
+# behavior cause the compiler_rt test to fail during try_compile: see
+# projects/compiler-rt/cmake/Modules/CompilerRTUtils.cmake:121 such that
+# CAN_TARGET_${arch} is not set properly. This results in COMPILER_RT_SUPPORTED_ARCH
+# not being updated properly leading to poblems.
+cmake_policy(SET CMP0056 OLD) 
 
 # FIXME: It may be removed when we use 2.8.12.
 if(CMAKE_VERSION VERSION_LESS 2.8.12)