enable cross compiling by adding option to remove -march/-cpu

CMakeLists.txt

@@ -35,6 +35,8 @@ 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_ENABLE_INSTRUMENTATION_OPT "Build rapidjson with -march or -mcpu options" ON)
+
 option(RAPIDJSON_HAS_STDSTRING "" OFF)
 if(RAPIDJSON_HAS_STDSTRING)
     add_definitions(-DRAPIDJSON_HAS_STDSTRING)
@@ -50,12 +52,14 @@ if(CCACHE_FOUND)
 endif(CCACHE_FOUND)
 
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+    if(${RAPIDJSON_DISABLE_INSTRUMENTATION_OPT}) 
         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 "${CMAKE_CXX_FLAGS} -march=native")
         endif()
+    endif()
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror")
     set(EXTRA_CXX_FLAGS -Weffc++ -Wswitch-default -Wfloat-equal -Wconversion -Wsign-conversion)
     if (RAPIDJSON_BUILD_CXX11)