SConstruct : Fix IECoreAppleseed build on Mac M1

Author: johnhaddon

SConstruct

@@ -3290,7 +3290,6 @@ appleseedEnvAppends = {
 	],
 	"CPPFLAGS" : [
 		"-DAPPLESEED_ENABLE_IMATH_INTEROP",
-		"-DAPPLESEED_USE_SSE",
 	],
 	"LIBPATH" : [
 		"$APPLESEED_LIB_PATH",
@@ -3299,6 +3298,9 @@ appleseedEnvAppends = {
 	],
 }
 
+if platform.machine() != "arm64" :
+	appleseedEnvAppends["CPPFLAGS"].append( "-DAPPLESEED_USE_SSE" )
+
 appleseedEnv.Append( **appleseedEnvAppends )
 
 appleseedPythonModuleEnv = pythonModuleEnv.Clone( **appleseedEnvSets )