cmake: move compiler checks into its own module

CMake/vtkCompilerChecks.cmake

+# Minimum compiler version check: GCC >= 4.8
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.8)
+  message(FATAL_ERROR "GCC 4.8 or later is required.")
+endif ()
+
+# Minimum compiler version check: LLVM Clang >= 3.3
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.3)
+  message(FATAL_ERROR "LLVM Clang 3.3 or later is required.")
+endif ()
+
+# Minimum compiler version check: Apple Clang >= 5.0 (Xcode 5.0)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+  message(FATAL_ERROR "Apple Clang 5.0 or later is required.")
+endif ()
+
+# Minimum compiler version check: Microsoft C/C++ >= 18.0 (aka VS 2013 aka VS 12.0)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0)
+  message(FATAL_ERROR "Microsoft Visual Studio 2013 or later is required.")
+endif ()
+
+# Minimum compiler version check: Intel C++ (ICC) >= 14
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Intel" AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 14.0)
+  message(FATAL_ERROR "Intel C++ (ICC) 14.0 or later is required.")
+endif ()
+
+# Make sure we have C++11 enabled.
+if(NOT VTK_IGNORE_CMAKE_CXX11_CHECKS)
+  # Needed to make sure libraries and executables not built by the
+  # vtkModuleMacros still have the C++11 compiler flags enabled
+  # Wrap this in an escape hatch for unknown compilers
+  set(CMAKE_CXX_STANDARD 11)
+  set(CMAKE_CXX_STANDARD_REQUIRED True)
+  set(CMAKE_CXX_EXTENSIONS False)
+endif()

CMakeLists.txt

@@ -9,51 +9,7 @@ project(VTK)
 set(VTK_CMAKE_DIR "${VTK_SOURCE_DIR}/CMake")
 set(CMAKE_MODULE_PATH ${VTK_CMAKE_DIR} ${CMAKE_MODULE_PATH})
 
-#-----------------------------------------------------------------------------
-# Minimum compiler version check: GCC >= 4.8
-if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.8)
-  message(FATAL_ERROR "GCC 4.8 or later is required.")
-endif ()
-
-#-----------------------------------------------------------------------------
-# Minimum compiler version check: LLVM Clang >= 3.3
-if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.3)
-  message(FATAL_ERROR "LLVM Clang 3.3 or later is required.")
-endif ()
-
-#-----------------------------------------------------------------------------
-# Minimum compiler version check: Apple Clang >= 5.0 (Xcode 5.0)
-if (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
-  message(FATAL_ERROR "Apple Clang 5.0 or later is required.")
-endif ()
-
-#-----------------------------------------------------------------------------
-# Minimum compiler version check: Microsoft C/C++ >= 18.0 (aka VS 2013 aka VS 12.0)
-if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0)
-  message(FATAL_ERROR "Microsoft Visual Studio 2013 or later is required.")
-endif ()
-
-#-----------------------------------------------------------------------------
-# Minimum compiler version check: Intel C++ (ICC) >= 14
-if (CMAKE_CXX_COMPILER_ID STREQUAL "Intel" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 14.0)
-  message(FATAL_ERROR "Intel C++ (ICC) 14.0 or later is required.")
-endif ()
-
-# Make sure we have C++11 enabled.
-if(NOT VTK_IGNORE_CMAKE_CXX11_CHECKS)
-  # Needed to make sure libraries and executables not built by the
-  # vtkModuleMacros still have the C++11 compiler flags enabled
-  # Wrap this in an escape hatch for unknown compilers
-  set(CMAKE_CXX_STANDARD 11)
-  set(CMAKE_CXX_STANDARD_REQUIRED True)
-  set(CMAKE_CXX_EXTENSIONS False)
-endif()
-
+include(vtkCompilerChecks)
 
 # Objective-C++ compile flags.
 # CMake has no equivalent of CMAKE_CXX_FLAGS for Objective-C++ (bug #4756)