Revert "Raising minimum required CMake version to 2.8.12.2."

This reverts commit r230062.

Debian stable (wheezy) ships still with cmake 2.8.9.

The commit broke my LLVM/Polly buildbot, to my knowledge our only Linux+cmake
buildbot.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230343 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -1,14 +1,24 @@
 # 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)
 
 if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
   message(STATUS "No build type selected, default to Debug")
   set(CMAKE_BUILD_TYPE "Debug")
 endif()
 
-if(POLICY CMP0022)
-  cmake_policy(SET CMP0022 NEW) # automatic when 2.8.12 is required
+# 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)

cmake/modules/LLVM-Config.cmake

@@ -41,9 +41,9 @@ function(explicit_llvm_config executable)
   llvm_map_components_to_libnames(LIBRARIES ${link_components})
   get_target_property(t ${executable} TYPE)
   if("x${t}" STREQUAL "xSTATIC_LIBRARY")
-    target_link_libraries(${executable} INTERFACE ${LIBRARIES})
+    target_link_libraries(${executable} ${cmake_2_8_12_INTERFACE} ${LIBRARIES})
   elseif("x${t}" STREQUAL "xSHARED_LIBRARY" OR "x${t}" STREQUAL "xMODULE_LIBRARY")
-    target_link_libraries(${executable} PRIVATE ${LIBRARIES})
+    target_link_libraries(${executable} ${cmake_2_8_12_PRIVATE} ${LIBRARIES})
   else()
     # Use plain form for legacy user.
     target_link_libraries(${executable} ${LIBRARIES})

lib/DebugInfo/PDB/CMakeLists.txt

@@ -73,4 +73,4 @@ add_llvm_library(LLVMDebugInfoPDB
   ${LIBPDB_ADDITIONAL_HEADER_DIRS}
   )
 
-target_link_libraries(LLVMDebugInfoPDB INTERFACE "${LIBPDB_ADDITIONAL_LIBRARIES}")
+target_link_libraries(LLVMDebugInfoPDB ${cmake_2_8_12_INTERFACE} "${LIBPDB_ADDITIONAL_LIBRARIES}")

lib/ExecutionEngine/Interpreter/CMakeLists.txt

@@ -13,7 +13,7 @@ add_llvm_library(LLVMInterpreter
   )
 
 if( LLVM_ENABLE_FFI )
-  target_link_libraries( LLVMInterpreter PRIVATE ${FFI_LIBRARY_PATH} )
+  target_link_libraries( LLVMInterpreter ${cmake_2_8_12_PRIVATE} ${FFI_LIBRARY_PATH} )
 endif()
 
 add_dependencies(LLVMInterpreter intrinsics_gen)

tools/llvm-shlib/CMakeLists.txt

@@ -90,7 +90,7 @@ if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux") # FIXME: It should be "GNU ld for el
   set(LIB_NAMES -Wl,--whole-archive ${LIB_NAMES} -Wl,--no-whole-archive)
 endif()
 
-target_link_libraries(LLVM PRIVATE ${LIB_NAMES})
+target_link_libraries(LLVM ${cmake_2_8_12_PRIVATE} ${LIB_NAMES})
 
 add_dependencies(LLVM libLLVMExports)