CMake: do not pass -march=native or -mcpu=native when crosscompiling

Author: DerDakon

CMakeLists.txt

@@ -52,7 +52,7 @@ if(CCACHE_FOUND)
 endif(CCACHE_FOUND)
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    if(RAPIDJSON_ENABLE_INSTRUMENTATION_OPT)
+    if(RAPIDJSON_ENABLE_INSTRUMENTATION_OPT AND NOT CMAKE_CROSSCOMPILING)
         if(CMAKE_SYSTEM_PROCESSOR STREQUAL "powerpc" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64le")
           set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mcpu=native")
         else()
@@ -84,11 +84,13 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
         endif()
     endif()
 elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    if(CMAKE_SYSTEM_PROCESSOR STREQUAL "powerpc" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64le")
-      set(CMAKE_CXX_FLAGS "${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 "${CMAKE_CXX_FLAGS} -march=native")
+    if(NOT CMAKE_CROSSCOMPILING)
+      if(CMAKE_SYSTEM_PROCESSOR STREQUAL "powerpc" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "ppc64le")
+        set(CMAKE_CXX_FLAGS "${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 -Wno-missing-field-initializers")
     set(EXTRA_CXX_FLAGS -Weffc++ -Wswitch-default -Wfloat-equal -Wconversion -Wimplicit-fallthrough)