Revert "Raising minimum required CMake version to 2.8.12.2."

This reverts commit add62ac.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228616 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -1,6 +1,20 @@
 # See docs/CMake.html for instructions about how to build LLVM with CMake.
 
-cmake_minimum_required(VERSION 2.8.12.2)
+cmake_minimum_required(VERSION 2.8.8)
+
+# FIXME: It may be removed when we use 2.8.12.
+if(CMAKE_VERSION VERSION_LESS 2.8.12)
+  # Invalidate a couple of keywords.
+  set(cmake_2_8_12_INTERFACE)
+  set(cmake_2_8_12_PRIVATE)
+else()
+  # Use ${cmake_2_8_12_KEYWORD} intead of KEYWORD in target_link_libraries().
+  set(cmake_2_8_12_INTERFACE INTERFACE)
+  set(cmake_2_8_12_PRIVATE PRIVATE)
+  if(POLICY CMP0022)
+    cmake_policy(SET CMP0022 NEW) # automatic when 2.8.12 is required
+  endif()
+endif()
 
 if(CMAKE_VERSION VERSION_LESS 3.1.20141117)
   set(cmake_3_2_USES_TERMINAL)