Update CMakeLists.txt

Author: mcbarton

CMakeLists.txt

@@ -128,7 +128,7 @@ function(configure_kernel kernel)
     string(REPLACE "\\" "/" XEUS_CPP_RESOURCE_DIR "${XEUS_CPP_RESOURCE_DIR}")
     string(REPLACE "\\" "/" XEUS_CPP_INCLUDE_DIR "${XEUS_CPP_INCLUDE_DIR}")
   endif()
-  if(NOT EMSCRIPTEN)
+  if(EMSCRIPTEN)
     set(prefix "wasm")
   else()
     set(XEUS_CPP_PATH "$ENV{PATH}")