zephyr/CMakeLists.txt: Properly separate CFLAGS parts gotten from CMake.

Lack of spaces between them led to weird option artifacts like -Ifoo-Dbar.

ports/zephyr/CMakeLists.txt

@@ -15,7 +15,7 @@ zephyr_get_compile_options_for_lang_as_string(C options)
 add_custom_target(
   outputexports
   COMMAND echo CC="${CMAKE_C_COMPILER}"
-  COMMAND echo Z_CFLAGS=${system_includes}${includes}${definitions}${options}
+  COMMAND echo Z_CFLAGS=${system_includes} ${includes} ${definitions} ${options}
   VERBATIM
   USES_TERMINAL
 )