STYLE: Allow use of clang-tidy as part of cmake compilation

Recent versions of cmake allow running clang-tidy as
part of the compilation process.

A <LANG>_CLANG_TIDY target property and supporting
CMAKE_<LANG>_CLANG_TIDY variable were introduced to tell the Makefile
Generators and the Ninja generator to run clang-tidy along with the
compiler for C and CXX languages.  Supported in cmake 3.6+.

.clang-tidy

@@ -0,0 +1,5 @@
+Checks: '-*,-modernize-use-using,-modernize-use-nullptr'
+CheckOptions:
+    - key:             modernize-use-nullptr.NullMacros
+      value:           NULL,CUSTOM_NULL
+FormatStyle: 'file'

CMake/ITKClangTidySetup.cmake

@@ -0,0 +1,29 @@
+# Provides itk_clangtidy_setup to assist with maintaining consistent
+# c++ best practices across the ITK toolkit
+#
+# Clang-tidy version 8.0 or greater is required
+#
+# The ITK C++ best practices guidelines are represented by clang-tidy
+# rules defined in ${ITK_SOURCE_DIR}/.clang-tidy
+#
+option(ITK_USE_CLANGTIDY "Enable the use of clang-tidy to enforce coding best practices." OFF)
+mark_as_advanced(ITK_USE_CLANGTIDY)
+
+if(ITK_USE_CLANGTIDY)
+  if ( ITK_USE_CLANGTIDY AND NOT EXISTS "${CLANGTIDY_EXECUTABLE}" )
+    find_program(CLANGTIDY_EXECUTABLE NAMES clang-tidy-13 clang-tidy-12 clang-tidy-11 clang-tidy-10 clang-tidy-9 clang-tidy-9 clang-tidy-8 clang-tidy )
+  endif()
+
+  if(CLANGTIDY_EXECUTABLE AND EXISTS "${CLANGTIDY_EXECUTABLE}")
+    mark_as_advanced(CLANGTIDY_EXECUTABLE)
+    set(CLANG_TIDY_CHECKS "-*,modernize-use-*")
+    set(CMAKE_CXX_CLANG_TIDY "${CLANGTIDY_EXECUTABLE};-checks=${CLANG_TIDY_CHECKS};-header-filter='${CMAKE_SOURCE_DIR}/Modules/*/*/include'")
+
+    # Compile commands are required by clang-tidy
+    set(CMAKE_EXPORT_COMPILE_COMMANDS ON CACHE BOOL "compile_commands.json file is needed by clang-tidy")
+  else()
+    unset(CLANGTIDY_EXECUTABLE)
+    unset(CMAKE_CXX_CLANG_TIDY)
+    message(FATAL_ERROR "Missing suitable clang-tidy executable, set CLANGTIDY_EXECUTABLE variable to desired path")
+  endif()
+endif()

CMakeLists.txt

@@ -529,6 +529,8 @@ include(ITKModuleEnablement)
 
 # Setup clang-format for code style enforcement
 include(ITKClangFormatSetup)
+# Setup clang-tidy for code best-practices enforcement for C++11
+include(ITKClangTidySetup)
 #----------------------------------------------------------------------
 # Generate ITKConfig.cmake for the build tree.
 set(ITK_CONFIG_CODE "