Use escaped variable preloaded files Emscripten build

Author: mcbarton

test/CMakeLists.txt

@@ -75,7 +75,7 @@ if(EMSCRIPTEN)
         PUBLIC "SHELL: -s EXIT_RUNTIME=1"
         PUBLIC "SHELL: -s STACK_SIZE=32mb"
         PUBLIC "SHELL: -s INITIAL_MEMORY=128mb"
-        PUBLIC "SHELL: --preload-file ${SYSROOT_PATH}/include@/include"
+        PUBLIC "SHELL: --preload-file ${ESCAPED_SYSROOT_PATH}/include@/include"
         PUBLIC "SHELL: --preload-file ../${XEUS_CPP_DATA_DIR}@/share/xeus-cpp"
         PUBLIC "SHELL: --preload-file ../${XEUS_CPP_CONF_DIR}@/etc/xeus-cpp"
         PUBLIC "SHELL: --emrun"