support IBM PowerPC / ppc64 / ppc64le and XL compiler

Avoid POWER platform compiling error and support IBM XL C++ compiler on
Linux / AIX.

CMakeLists.txt

@@ -50,7 +50,13 @@ if(CCACHE_FOUND)
 endif(CCACHE_FOUND)
 
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native -Wall -Wextra -Werror")
+    if(${CMAKE_SYSTEM_PROCESSOR} STREQUAL "powerpc" OR ${CMAKE_SYSTEM_PROCESSOR} STREQUAL "ppc64" OR ${CMAKE_SYSTEM_PROCESSOR} STREQUAL "ppc64le")
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mcpu=native")
+    else()
+      #FIXME: x86 is -march=native, but doesn't mean every arch is this option. To keep original project's compatibility, I leave this except POWER.
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native")
+    endif()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror")
     if (RAPIDJSON_BUILD_CXX11)
         if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.7.0")
             set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
@@ -73,7 +79,13 @@ if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
         endif()
     endif()
 elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native -Wall -Wextra -Werror -Wno-missing-field-initializers")
+    if(${CMAKE_SYSTEM_PROCESSOR} STREQUAL "powerpc" OR ${CMAKE_SYSTEM_PROCESSOR} STREQUAL "ppc64" OR ${CMAKE_SYSTEM_PROCESSOR} STREQUAL "ppc64le")
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mcpu=native")
+    else()
+      #FIXME: x86 is -march=native, but doesn't mean every arch is this option. To keep original project's compatibility, I leave this except POWER.
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native")
+    endif()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror -Wno-missing-field-initializers")
     if (RAPIDJSON_BUILD_CXX11)
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
     endif()
@@ -90,6 +102,8 @@ elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
     add_definitions(-D_CRT_SECURE_NO_WARNINGS=1)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /EHsc")
+elseif (CMAKE_CXX_COMPILER_ID MATCHES "XL")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -qarch=auto")
 endif()
 
 #add extra search paths for libraries and includes