support building with ASAN and UBSAN on Clang and GCC

CMakeLists.txt

 CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
+if(POLICY CMP0025)
+  # detect Apple's Clang
+  cmake_policy(SET CMP0025 NEW)
+endif()
 if(POLICY CMP0054)
   cmake_policy(SET CMP0054 NEW)
 endif()
@@ -28,6 +32,9 @@ option(RAPIDJSON_BUILD_THIRDPARTY_GTEST
 
 option(RAPIDJSON_BUILD_CXX11 "Build rapidjson with C++11 (gcc/clang)" ON)
 
+option(RAPIDJSON_BUILD_ASAN "Build rapidjson with address sanitizer (gcc/clang)" OFF)
+option(RAPIDJSON_BUILD_UBSAN "Build rapidjson with undefined behavior sanitizer (gcc/clang)" OFF)
+
 option(RAPIDJSON_HAS_STDSTRING "" OFF)
 if(RAPIDJSON_HAS_STDSTRING)
     add_definitions(-DRAPIDJSON_HAS_STDSTRING)
@@ -51,11 +58,35 @@ if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
             set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
         endif()
     endif()
+    if (RAPIDJSON_BUILD_ASAN)
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.8.0")
+            message(FATAL_ERROR "GCC < 4.8 doesn't support the address sanitizer")
+        else()
+            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=address")
+        endif()
+    endif()
+    if (RAPIDJSON_BUILD_UBSAN)
+        if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.9.0")
+            message(FATAL_ERROR "GCC < 4.9 doesn't support the undefined behavior sanitizer")
+        else()
+            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=undefined")
+        endif()
+    endif()
 elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native -Wall -Wextra -Werror -Wno-missing-field-initializers")
     if (RAPIDJSON_BUILD_CXX11)
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
     endif()
+    if (RAPIDJSON_BUILD_ASAN)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=address")
+    endif()
+    if (RAPIDJSON_BUILD_UBSAN)
+        if (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
+            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=undefined-trap -fsanitize-undefined-trap-on-error")
+        else()
+            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=undefined")
+        endif()
+    endif()
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
     add_definitions(-D_CRT_SECURE_NO_WARNINGS=1)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /EHsc")