Print a warning message if compiler-rt can't be built because of old CMake version to make this requirement more visible to users

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176481 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Alexey Samsonov

projects/CMakeLists.txt

@@ -13,7 +13,10 @@ endforeach(entry)
 
 # Also add in the compiler-rt tree if present and we have a sufficiently
 # recent version of CMake.
-if(${CMAKE_VERSION} VERSION_GREATER 2.8.7 AND
-   ${LLVM_BUILD_RUNTIME})
-  add_llvm_external_project(compiler-rt)
+if(${LLVM_BUILD_RUNTIME})
+  if(${CMAKE_VERSION} VERSION_GREATER 2.8.7)
+    add_llvm_external_project(compiler-rt)
+  else()
+    message(WARNING "Can't build compiler-rt, CMake 2.8.8 required!")
+  endif()
 endif()